Normal temperature asphalt mortar and mixture with desulfurized gypsum as filler

Abstract

The present application relates to a kind of normal temperature pitch mastic with desulfurization gypsum as filler, it contains filler, curing agent and normal temperature pitch;Filler is the mixture of desulfurization gypsum and limestone powder;Desulfurization gypsum is pretreated by high temperature oxidation;The mass ratio of filler and normal temperature pitch is 0.8-1.1:1;Curing agent is the mixture of Portland cement and metakaolin, its dosage is 15-25% of normal temperature pitch;Normal temperature pitch is reactive normal temperature liquid pitch, is to flow to the matrix pitch of adding reactive liquid agent and modifier water-based epoxy resin emulsion and is prepared by shearing mixing;Reactive liquid agent is to use unsaturated fatty acid as liquid agent matrix material, add zwitterionic surfactant and phenol polymer and is prepared by stirring mixing.The present application can reduce the dependence on limestone on the one hand, on the other hand, the desulfurization gypsum of large amount of solid waste of thermal power plant can be reduced and recycled, and test proves that the pitch mastic has good road performance.

Description

Technical Field

[0001] This invention relates to the field of ambient temperature asphalt mixture technology, and in particular to an ambient temperature asphalt mortar and mixture using desulfurized gypsum as filler. Background Technology

[0002] Currently, most high-grade roads use asphalt mixtures, which are made by mixing asphalt as a binder, mineral aggregates with a certain gradation, fillers, and admixtures. A common filler is limestone powder, which is made from limestone through grinding and other processing. However, natural stone is a non-renewable resource in the short term, and limestone mining exposes mountainsides and damages natural vegetation, negatively impacting the local environment and ecosystem. Meanwhile, with the promotion and application of desulfurization technology, the production of desulfurization gypsum, a solid waste from thermal power plants, has increased rapidly. The accumulation of desulfurization gypsum occupies a large amount of land resources, and its disposal urgently needs to be addressed. Therefore, if desulfurization gypsum could be used as a filler in asphalt mixtures, it would reduce the mining of natural limestone and also allow for the reuse of desulfurization gypsum solid waste resources—a win-win situation. Currently, desulfurized gypsum is mainly used in the preparation of gypsum blocks, as roadbed backfill material, and plastering, but there are no reports on relevant schemes for using desulfurized gypsum as filler in asphalt mixtures or on the application performance of asphalt mixtures.

[0003] Meanwhile, hot-mix asphalt mixtures, as one of the most widely used building materials in the road industry, consume a large amount of energy during their manufacturing and paving processes. Hot-mix asphalt mixtures typically require mixing and paving at temperatures up to 180℃, releasing large amounts of asphalt fumes and greenhouse gases, causing serious environmental pollution. Furthermore, the temperature during construction of hot-mix asphalt mixtures needs strict control and is greatly affected by weather conditions. Given these shortcomings of hot-mix asphalt mixtures, it is necessary to develop a room-temperature asphalt mixture that does not require high-temperature heating. Replacing hot-mix asphalt mixtures with a room-temperature asphalt mixture for road construction would be of great significance for reducing construction costs, saving energy and reducing emissions, and protecting the environment. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a room-temperature asphalt mortar and mixture using desulfurized gypsum as filler. The method involves mixing desulfurized gypsum with room-temperature asphalt, simultaneously adding a selected curing agent to prepare the room-temperature asphalt mortar, and then mixing the mortar with mineral aggregates, fillers, etc., at room temperature to obtain the room-temperature asphalt mixture. Road performance tests show that this mixture can be mixed and paved at room temperature, exhibiting good water loss resistance, high-temperature shear resistance, and low-temperature crack resistance, among other road performance characteristics. This not only reduces the mining of natural limestone but also enables the reuse of desulfurized gypsum solid waste resources, thus possessing significant environmental protection value.

[0006] (II) Technical Solution

[0007] In a first aspect, the present invention provides a room temperature asphalt mortar using desulfurized gypsum as filler, which contains: filler, curing agent and room temperature asphalt;

[0008] The filler is a mixture of desulfurized gypsum and limestone powder, wherein the desulfurized gypsum accounts for 0.1-99.9% of the filler mass; the desulfurized gypsum undergoes high-temperature oxidation pretreatment.

[0009] The mass ratio of filler to room temperature asphalt is 0.8-1.1:1; the curing agent is a mixture of silicate cement and metakaolin, and the amount of curing agent is 15-25% of the mass of room temperature asphalt.

[0010] The ambient temperature asphalt is a reactive ambient temperature liquid asphalt, which is prepared by adding a reactive liquefying agent and a modifier aqueous epoxy resin emulsion to a fluid matrix asphalt and then shearing and mixing them. The reactive liquefying agent is prepared by adding unsaturated fatty acids as the liquefying agent matrix material and adding zwitterionic surfactants and phenol polymers and stirring and mixing them.

[0011] According to a preferred embodiment of the present invention, the mass fraction of desulfurized gypsum in the filler is 10-90%, preferably 30-70%, more preferably 30% or 70%. When desulfurized gypsum accounts for 70% of the total filler, the asphalt mastic exhibits optimal low-temperature performance (mainly low-temperature crack resistance), with the maximum peak value of low-temperature performance appearing at this dosage. Evaluation of the adhesion performance of the asphalt mastic using the boiling water method shows that when desulfurized gypsum accounts for 70% of the total filler, it can significantly improve the adhesion between the asphalt mastic and aggregates, and increase the strength of the asphalt mastic material. Furthermore, penetration and softening point test results indicate that, at the same temperature, continuously increasing the dosage of desulfurized gypsum makes the asphalt mastic more effective in improving its high-temperature performance. SDR test results show that the addition of desulfurized gypsum can improve the shear deformation resistance of the asphalt mastic and increase the viscous components in the asphalt mastic, thus enhancing its rutting resistance. When the mass fraction of desulfurized gypsum in the filler is 30%, the cohesiveness of the asphalt mixture at room temperature is the highest, and the freeze-thaw splitting residual strength ratio reaches its peak value.

[0012] Desulfurized gypsum, also known as flue gas desulfurization gypsum, FGD gypsum, or sulfur gypsum, has the same main component as natural gypsum, CaSO4·2H2O. It is an industrial byproduct obtained from the treatment of SO2 flue gas in industrial applications. Due to inaccurate temperature control during the desulfurization process, it also contains small amounts of byproducts such as CaCO3, CaSO3, and CaSO4·1 / 2H2O. To improve the stability of desulfurized gypsum and avoid instability at mixing temperatures, decomposition, and the release of sulfur dioxide causing secondary pollution, further measures are needed. Additionally, calcium sulfite reacts with oxygen in the air, causing volume expansion, and hemihydrate gypsum undergoes a hydration reaction with water, releasing heat and also easily causing volume expansion. Therefore, desulfurized gypsum cannot be directly applied to asphalt mortar and mixtures, as this can easily lead to road surface cracking.

[0013] In a preferred embodiment of the present invention, in order to ensure the application strength of asphalt mastic and asphalt mixture, when using desulfurized gypsum as a filler component of room temperature asphalt mastic, the desulfurized gypsum should be pretreated to ensure that the desulfurized gypsum remains stable and does not decompose during the preparation of asphalt mastic. The pretreatment method for desulfurized gypsum is as follows: heat the desulfurized gypsum in an air atmosphere at 115-124°C and allow it to react fully for at least 2 hours.

[0014] According to a preferred embodiment of the present invention, the filler preparation method is as follows: pretreated desulfurized gypsum and limestone powder are passed through a 0.075mm sieve and the undersize portion is taken. The mixture is then dried in an oven at 120-124℃ for more than 3 hours to remove free water and bound water (partially bound water can be removed) from the desulfurized gypsum and limestone powder.

[0015] According to a preferred embodiment of the present invention, the mass ratio of the filler to room temperature asphalt is 1:1.

[0016] According to a preferred embodiment of the present invention, the mass ratio of silicate cement to metakaolin in the curing agent is 2:1.

[0017] The reactive liquefaction agent for room-temperature liquid asphalt is unsaturated fatty acid, the modifier is water-based epoxy resin emulsion, and silicate cement is an alkaline substance. On one hand, silicate cement can chemically react with the unsaturated fatty acid, causing the reactive liquefaction agent to lose its liquefaction ability at room temperature. On the other hand, silicate cement also has a strong water absorption capacity, absorbing moisture from the water-based epoxy resin emulsion, causing the epoxy resin to connect and form a dense network structure. Metakaolin is an inorganic active powder. In a humid environment, it forms a volcanic ash effect with silicate cement, chemically binding with the asphalt film on its own surface. This interaction manifests as wetting, adsorption, and chemical reaction. These three effects make the inorganic active powder more easily adsorbed onto the asphalt layer surface and increase the viscosity of the residual asphalt, also improving the road performance of room-temperature liquid asphalt mixtures to some extent. Because metakaolin is a fine spherical active inorganic powder, it also has excellent filling properties, filling the small voids in the mixture as a filler.

[0018] According to a preferred embodiment of the present invention, the curing agent dosage is 19-21% of the mass of room temperature asphalt, preferably 20%. A comprehensive comparison of the three indicators—penetration, softening point, and ductility—shows that as the curing agent dosage increases, the penetration decreases continuously and at a slower rate; the softening point increases with increasing curing agent dosage, but the rate of increase gradually slows; however, ductility is neither positively nor negatively correlated with the dosage. Specifically, as the curing agent dosage increases, the ductility first increases and then decreases, reaching a peak at 20% of the room temperature asphalt dosage, corresponding to a ductility value of 7.84 cm at 5°C. The silicate cement in the curing agent is a hydraulic gel material, which improves the high-temperature rheological properties of the cured residual asphalt, specifically manifested as an increase in softening point and penetration. However, excessive curing agent addition negatively impacts the low-temperature performance of the residual asphalt, resulting in a phenomenon where the ductility first increases and then decreases. Therefore, the curing agent dosage is preferably determined to be 19-21 wt.% of the room temperature asphalt, and more preferably 20 wt.%.

[0019] According to a preferred embodiment of the present invention, the reactive room-temperature liquid asphalt is prepared by adding 20-30 parts by weight of a reactive liquefying agent and 10-20 parts by weight of a water-based epoxy resin emulsion modifier to 50-60 parts by weight of a base asphalt that has been heated to a fluid state at high temperature, followed by shearing and stirring. The reactive liquefying agent is prepared by adding alkyl dimethyl betaine and phenol polymer as the liquefying agent matrix material, followed by stirring and mixing. The mass ratio of unsaturated fatty acid:alkyl dimethyl betaine:phenol polymer is 15-25:5-10:1-5. The unsaturated fatty acid is at least one selected from myristoleic acid, trans-oleic acid, oleic acid, linoleic acid, erucic acid, palmitoleic acid, and ricinoleic acid. The alkyl dimethyl betaine is a C10-20 alkyl dimethyl betaine. The phenol polymer is tris-(dimethylaminomethyl)phenol polymer. The related technology of reactive room-temperature liquid asphalt is a technology previously developed by the inventors' team and has been patented.

[0020] According to a preferred embodiment of the present invention, 10-20 parts by weight of a coupling agent are also added to the reactive room temperature liquid asphalt, wherein the coupling agent is a silane coupling agent, preferably a C10-20 alkyltriethoxysilane.

[0021] Thirdly, the present invention also provides a room-temperature asphalt mixture using desulfurized gypsum as filler, which includes room-temperature asphalt mortar and aggregates from any of the above embodiments.

[0022] Preferably, the aggregate is an AC or SMA graded aggregate, such as AC-13, AC-16, SMA-13, or SMA-16, and more preferably AC-16.

[0023] Preferably, the room temperature asphalt is 4.6-6.6% of the mineral aggregate mass, more preferably 5-6%, and even more preferably 5.6%.

[0024] Fourthly, the present invention also relates to the application of room temperature asphalt mixtures with desulfurized gypsum as filler in road paving and pothole repair.

[0025] Experiments show that this ambient temperature asphalt mixture has good workability, high initial strength (around 5kN), and high molding stability (greater than 12kN), fully meeting the technical indicators for pothole repair material stability. The addition of more desulfurized gypsum increases the volume ratio of asphalt mortar to adhesive mortar in the mixture, allowing it to fill more of the voids. Therefore, as the amount of desulfurized gypsum increases, the molding stability also gradually increases, comparable to the molding stability of hot-mix asphalt mixtures commonly used for pothole repair on the market. Furthermore, this ambient temperature asphalt mixture features simple construction, easy control, significantly reduced emissions of toxic gases, extended construction season, less demanding weather requirements, long-distance transportation capability, and ease of construction.

[0026] (III) Beneficial Effects

[0027] This invention uses desulfurized gypsum to replace or partially replace limestone powder as a filler in asphalt mortar to produce room-temperature asphalt mortar. On the one hand, it can reduce dependence on limestone and reduce the negative impact of limestone mining on the natural environment and ecosystem. On the other hand, it can reduce the volume of desulfurized gypsum, a large amount of solid waste from thermal power plants, reduce stockpiling, save land resources, and realize the resource reuse of desulfurized gypsum solid waste.

[0028] Desulfurized gypsum has a small particle size and a large specific surface area. It can replace or partially replace limestone aggregates and be mixed into room temperature asphalt through shearing action. Desulfurized gypsum and room temperature reactive asphalt can combine to form asphalt mortar with high viscosity. This invention further optimizes parameters such as the dosage of desulfurized gypsum and the composition and dosage of curing agent to make the asphalt mortar have better high-temperature and low-temperature performance (high high-temperature hardness, low-temperature crack resistance), shear deformation resistance, better adhesion to mineral aggregates, and enhanced rutting resistance.

[0029] Furthermore, by mixing the ambient temperature asphalt mortar with mineral aggregates of a certain gradation, an ambient temperature asphalt mixture is prepared. After molding, this mixture exhibits high early strength and molding stability, comparable to the molding stability of hot-mix asphalt mixtures commonly used for pothole repair. In addition, ambient temperature asphalt is produced by adding specific solvents to the base asphalt. Due to solvent evaporation, ambient temperature asphalt mixtures experience some shrinkage in the early stages of curing. However, by using desulfurized gypsum as a filler, the micro-expansion effect of the desulfurized gypsum can further reduce the early shrinkage problem of the ambient temperature asphalt curing system.

[0030] By optimizing parameters such as the gradation of the mineral aggregates and the content of room-temperature asphalt in the mixture, the initial stability and molding stability of the mixture meet the technical specifications, and increase with the increase of desulfurized gypsum content. When the ratio of desulfurized gypsum to limestone powder is 7:3, the dynamic stability reaches 4615 cycles / min. Marshall tests and freeze-thaw splitting tests show that when the ratio of desulfurized gypsum to limestone powder is 3:7, the asphalt mixture has the best water stability, cohesiveness, and bonding performance. In addition, the tests also proved that desulfurized gypsum has a small negative impact on workability and skid resistance. The asphalt mixture can be mixed and laid at room temperature, with low energy consumption, no large amount of asphalt fumes or room temperature gas release, no strict requirements on construction conditions, and advantages such as easy control, no need for high-temperature heating, and environmental friendliness.

[0031] In conclusion, using desulfurized gypsum as a filler to replace limestone powder in ambient temperature asphalt mixtures can, on the one hand, reduce the mining of natural stone, greenhouse gas emissions, protect the ecological environment, and reduce the construction cost of asphalt pavements; on the other hand, it also provides a new approach to the disposal of desulfurized gypsum, solving the problem of land occupation caused by its accumulation, and has significant economic implications and broad market prospects. Attached Figure Description

[0032] Figure 1 The penetration of five groups of desulfurized gypsum-room temperature asphalt mortar in Examples 1-5 was tested at 25°C.

[0033] Figure 2 The softening point of five groups of desulfurized gypsum-room temperature asphalt mortar in Examples 1-5 was tested at 25°C.

[0034] Figure 3 The rutting factor (G* / sinδ) of the original asphalt of the five groups of desulfurized gypsum-room temperature asphalt mortar in Examples 1-5.

[0035] Figure 4 The rutting factor (G* / sinδ) of the asphalt after RTFOT for the five groups of desulfurized gypsum-room temperature asphalt mortar in Examples 1-5 is given.

[0036] Figure 5 The results are the low-temperature rheological properties (BBR test) of the five groups of desulfurized gypsum-room temperature asphalt mortars in Examples 1-5.

[0037] Figure 6 The results of the adhesion test of desulfurized gypsum-room temperature asphalt mortar in Examples 1-5 (residual asphalt mortar mass ratio RRA) are shown.

[0038] Figure 7 The ductility (a), penetration (b), and softening point (c) of four groups of desulfurized gypsum (actual content 0)-room temperature asphalt mortar in Examples 6-10 are shown.

[0039] Figure 8 The figure shows the median curves of the four gradations of aggregates used in the ambient temperature asphalt mixtures in Examples 10-13.

[0040] Figure 9 This is a graph showing the Marshall test stability of the ambient temperature asphalt mixture in Example 14 as a function of gradient, representing the asphalt content.

[0041] Figure 10 This is a schematic diagram of the low-temperature bending creep performance test operation in Example 15. Detailed Implementation

[0042] To better explain and facilitate understanding of the present invention, a detailed description of the invention is provided below with reference to the accompanying drawings and specific embodiments. In the following embodiments, unless otherwise specified, the number of parts refers to parts by weight, and if the material ratio is not specified, it refers to the mass ratio.

[0043] Example 1

[0044] The room-temperature asphalt mortar with desulfurized gypsum as filler provided in this embodiment is prepared by the following method:

[0045] (1) Preparation of filler: Desulfurized gypsum was heated in air at 120°C for 2 hours to allow it to react fully. The gypsum was then passed through a 0.075 mm sieve, and the undersize portion was collected. Limestone powder was also passed through a 0.075 mm sieve, and the undersize portion was collected. A filler was prepared by mixing desulfurized gypsum and limestone powder in a 5:5 mass ratio and then dried in an oven at 120°C for 3 hours to remove free and bound water from the desulfurized gypsum and limestone powder.

[0046] Experiments have confirmed that, through pretreatment, the calcium sulfite in the desulfurized gypsum is converted into calcium sulfate by the evaporation of free water and bound water. It exhibits good stability at the working temperature of asphalt at room temperature (usually around 60°C), with no obvious exothermic or endothermic reactions occurring. This indicates that the desulfurized gypsum is stable after pretreatment and does not affect the performance of asphalt mortar even under hot climatic conditions.

[0047] (2) Preparation of curing agent: Take commercially available PO42.5 silicate cement (Wuxi Jianghuai Building Materials Science and Technology Co., Ltd.) and ultrafine metakaolin (Shijiazhuang Huabang) and mix them in a mass ratio of 2:1.

[0048] (3) Room temperature asphalt: 55 parts of base asphalt (Donghai brand 90# base asphalt) were heated to 140℃, and 22 parts of reactive liquefaction agent and 12 parts of water-based epoxy resin emulsion (solid content 50%) were added under shear stirring at 50-80 rpm. The mixture was stirred for 15 minutes until it was completely dispersed and uniform to obtain room temperature asphalt. The reactive liquefaction agent was prepared by mixing ricinoleic acid, dodecyl dimethyl betaine, and tris-(dimethylaminomethyl)phenol polymer in a mass ratio of 10:3:1.5.

[0049] The grade of the base asphalt can be used as a preliminary screening standard for asphalt. The smaller the grade, the harder the base asphalt is and the better its high-temperature performance. The larger the grade, the higher the softening rate, the higher the ductility, and the better the low-temperature performance. Donghai brand 90# base asphalt is a base asphalt with good low-temperature performance. Its softening point is ≥48℃, the penetration (25℃, 100g, 5s, 0.1mm) is about 90, the ductility (15℃) is ≥100cm, the relative density is 1.038, the mass change % after TFOF is -0.35, the residual penetration ratio after TFOF is ≥57.8cm, and the residual ductility (15℃) after TFOF is ≥10.8cm.

[0050] (4) Preheat the filler and curing agent to 60°C. According to the filler to room temperature asphalt mass ratio of 1:1 and the curing agent amount of 20% of room temperature asphalt, the filler powder and curing agent powder are mixed into the room temperature asphalt. The mixture is stirred for 15 minutes at 1800 rpm and 60°C using a high-speed shearing apparatus, and then stirred at 3000 rpm for 20 minutes to obtain room temperature asphalt mortar with desulfurized gypsum as filler.

[0051] Examples 2-5

[0052] Examples 2-5 are based on Example 1, with the mixing ratio of desulfurized gypsum and limestone powder changed to 0:10, 3:7, 7:3 and 10:0 respectively to obtain four fillers. The fillers are mixed with room temperature asphalt at a ratio of 1:1 to obtain the corresponding asphalt mortar.

[0053] The asphalt mortars of Examples 1-5 are recorded as follows:

[0054]

[0055] The performance of the five types of asphalt mastics were tested, including the following aspects:

[0056] (1) Penetration and softening point

[0057] Penetration of five groups of desulfurized gypsum-room-temperature asphalt mortar was tested at 25℃. The test results are shown below. Figure 1 As shown in the figure, the penetration decreases with increasing addition of desulfurized gypsum. A smaller penetration indicates a higher viscosity and harder asphalt mortar. This is mainly because, compared to limestone powder, desulfurized gypsum has a larger contact area with room-temperature asphalt, increasing internal friction and thus reducing penetration.

[0058] The softening point of five groups of desulfurized gypsum-room-temperature asphalt mortar was tested, and the test results are as follows: Figure 2 As shown in the figure, increasing the amount of desulfurized gypsum leads to an increase in the softening point. When the ratio of desulfurized gypsum to limestone powder is 10:0, the softening point of the asphalt mortar at room temperature is 54.3℃. This indicates that incorporating desulfurized gypsum can improve the high-temperature deformation resistance of asphalt at room temperature.

[0059] (2) Dynamic shear rheology (DSR test) performance

[0060] Dynamic shear rheology is used to evaluate the high-temperature load-bearing capacity of asphalt compounds. Asphalt pavement materials with poor high-temperature load-bearing capacity are prone to high-temperature distress such as rutting and subsidence under high temperatures and sustained loads. The dynamic shear rheology test (DSR) was used to test the complex shear modulus (G* and phase angle δ) and rutting factor (G* / sinδ) of undisturbed asphalt and the residual asphalt after aging in a rotating thin film oven test (RTFOT) to evaluate the high-temperature load-bearing capacity of asphalt compounds. Test results are shown in [link to test results]. Figure 3 and Figure 4 , Figure 3 The rutting factor (G* / sinδ) of the original asphalt sample. Figure 4 The rutting factor (G* / sinδ) is the rutting factor of the asphalt after RTFOT.

[0061] The rutting factor indicates the asphalt binder's ability to resist high-temperature deformation. Studies show that a larger rutting factor indicates better resistance to high-temperature deformation in the asphalt binder. Figure 3-4 It can be seen that the rutting factor (G* / sinδ) value of the (RTFOT) aged asphalt mortar is greater than that of the original asphalt mortar. Furthermore, within 50℃, the rutting factor (G* / sinδ) value in the original asphalt mortar increases with the increase of the desulfurized gypsum incorporation ratio. After 50℃, the rutting factors of the various asphalt mortars are basically overlapping. Therefore, when testing below 50℃, using desulfurized gypsum and limestone powder as fillers, a higher proportion of desulfurized gypsum incorporation results in stronger resistance to rutting deformation. When testing above 50℃, the mixing ratio of desulfurized gypsum and limestone powder has no significant effect on the rutting factor.

[0062] (3) Low-temperature rheological properties (BBR test: low-temperature bending beam rheological test)

[0063] Low-temperature rheological properties are an indicator for evaluating the low-temperature deformation resistance of asphalt mastic. The standard is a creep stiffness not exceeding 300 MPa and a creep rate not less than 0.3 after a 60-second load application time. Creep stiffness represents the asphalt's ability to resist dead load at low temperatures, while creep rate characterizes the rate of change of the stiffness modulus of the beam under load. The smaller the creep stiffness and the larger the creep rate at low temperatures, the better the crack resistance of the asphalt. The test conditions for this experiment were selected as -18℃, -12℃, and -6℃. The test results are as follows: Figure 5 As shown in a) and b).

[0064] Depend on Figure 5It can be seen that the stiffness modulus values ​​of the asphalt mastic in Examples 2 and 5 are relatively close. The test data of the bending beam rheological test of the five asphalt mastics are also relatively close at a temperature of -6℃, with creep stiffness modulus ranging from 75MPa to 115MPa and creep rate ranging from 0.49 to 0.54. From the curves in the figure, it can be observed that as the test temperature decreases, the difference in creep stiffness modulus at the same temperature level gradually increases, while the creep rate gradually decreases. Furthermore, the creep stiffness modulus and creep rate do not show a linear relationship with the amount of desulfurized gypsum added; the creep stiffness modulus of the asphalt mastic in Examples 1-4 decreases with increasing desulfurized gypsum addition, while the creep rate increases with increasing desulfurized gypsum addition. This is mainly because the density of desulfurized gypsum is less than that of limestone powder. Under the same mass, the volume of desulfurized gypsum is greater than that of limestone powder, and the specific surface area of ​​desulfurized gypsum is much greater than that of limestone powder. Therefore, when the amount of desulfurized gypsum is small, the component that interacts with asphalt in the asphalt mortar is mainly limestone powder. However, as the amount of desulfurized gypsum increases, the contact area between the filler and the asphalt increases, and more desulfurized gypsum in the asphalt mortar can continuously interact with the asphalt to transform it into structural asphalt. This process helps the asphalt mortar to form a more stable and stronger structure, which is reflected in the linear change between the test results of the four asphalt mortars in Examples 1-4 and the amount of desulfurized gypsum at the same temperature.

[0065] When the content of desulfurized gypsum exceeds 70%, the values ​​of the parabolic stiffness modulus and creep rate show a turning point, with the data curves exhibiting their maximum peak values. This is because as the content of desulfurized gypsum increases, the volume of the filler also gradually increases. This increased volume of desulfurized gypsum makes it difficult to mix evenly with the asphalt binder, resulting in poor dispersion and varying degrees of agglomeration throughout the asphalt mortar. Consequently, the asphalt mortar becomes brittle and hard, loses its stress relaxation properties, and its rheological properties actually decrease. Therefore, when the proportion of desulfurized gypsum in the filler reaches 70%, the low-temperature performance of the asphalt mortar is optimal; if it exceeds 70%, it will weaken the low-temperature fracture resistance of the asphalt mortar.

[0066] (4) Adhesion (residual bitumen mass ratio RRA test)

[0067] Adhesion is an indicator of the adhesion of asphalt mastic to mineral aggregates, and can be tested using the boiling water method. This experiment used limestone as coarse aggregate, with a particle size of 13.2-19 mm. After cleaning, the aggregate was dried at 105℃. The aggregate was tied securely with a thin thread, and the particles were immersed in asphalt mastic for 45 seconds to ensure complete surface coating. The particles were then removed, suspended for 15 minutes, cooled, and placed in boiling water. The boiling water was then simmered for 3 minutes. The degree of asphalt mastic peeling off the surface of the coarse aggregate particles was measured, and the residual asphalt mastic mass ratio (RRA) was calculated.

[0068]

[0069] Test results are as follows Figure 6 As shown in the figure, the Residual Amount (RRA) gradually increases with the increase of desulfurized gypsum content, and the rate of increase also gradually increases. When desulfurized gypsum is fully added, the RRA of the asphalt mastic is 61.6%, which is about 40% higher than that of the asphalt mastic with full limestone powder (Example 2). This is mainly because desulfurized gypsum has a larger specific surface area and lower density, allowing the asphalt mastic to be better adsorbed onto its surface and less likely to fall off during boiling. When the desulfurized gypsum content is 70% and 100%, the mass ratio of residual asphalt mastic on the aggregate surface exceeds 50%. It is evident that with the addition of desulfurized gypsum, the adhesion performance between the aggregate and the asphalt mastic is significantly improved, further enhancing the strength of the asphalt mastic material. This also provides a theoretical basis for the subsequent preparation of ambient temperature asphalt mixtures with added mineral aggregates.

[0070] Examples 6-9

[0071] Examples 6-9 describe the following: When the desulfurized gypsum content is 5% (the mass ratio of desulfurized gypsum to limestone powder is 5:95), the amount of curing agent added is varied to 10% (Example 6), 15% (Example 7), 25% (Example 8), and 20% (Example 9); the ductility at 5°C (5 cm / min, unit: cm), penetration (25°C, 100g, 5s, unit: 0.1mm), and softening point (ring and ball method, unit: °C) of the asphalt mastic are tested, and the results are as follows: Figure 7 As shown in a), b) and c).

[0072] Depend on Figure 7 It is known that the greater the amount of curing agent added, the smaller the penetration and the higher the softening point. As the amount of curing agent added increases, the ductility index first increases and then decreases, reaching its peak at around 20%, where the ductility at 5℃ is 7.84 cm. The curing agent used in this invention operates on the principle that: when inorganic active powder is mixed with the aqueous epoxy emulsion in reactive room-temperature asphalt, a pozzolanic effect occurs, causing the unsaturated fatty acids in the reactive room-temperature asphalt to become unstable under alkaline conditions, increasing the interaction between asphalt molecules and raising the viscosity. With the occurrence of the pozzolanic effect, the inorganic active powder will gradually undergo a hydration reaction, producing a large number of hard particle crystals that fill the voids in the residual asphalt, making the cured residual asphalt brittle and hard, achieving the purpose of room-temperature asphalt curing. However, the addition of excessive inorganic active powder will negatively affect the low-temperature performance of the residual asphalt, resulting in a phenomenon where the ductility first increases and then decreases. Therefore, in order to balance the high-temperature performance, viscosity and plasticity of asphalt adhesive, the content of curing agent is set at around 20%, which can be 15-25%, preferably 19-21%, and optimally 20%.

[0073] It should be noted that the above example only illustrates the preparation of a curing agent using silicate cement and ultrafine metakaolin in a 2:1 ratio, but this does not mean that the curing agent can only be prepared in this ratio. In actual production, this ratio can be appropriately adjusted according to the properties of the asphalt at room temperature, the content of reactive liquefaction agent, the amount of waterborne epoxy resin emulsion added, and the solid content index. When the amount of waterborne epoxy resin emulsion added is high or its solid content is low, the proportion of ultrafine metakaolin can be appropriately increased. When the content of unsaturated fatty acids introduced by the reactive liquefaction agent is high, the proportion of silicate cement can be appropriately increased. Preferably, in the curing agent, the mass ratio of silicate cement to ultrafine metakaolin can be between 1.8 and 2.2:1.

[0074] Examples 10-13

[0075] This embodiment uses room-temperature asphalt mortar as a base, which is mixed with mineral aggregates to obtain a road-ready room-temperature asphalt mixture. During the preparation of the room-temperature asphalt mixture, to avoid rapid curing of the room-temperature asphalt mortar, the curing agent in the room-temperature asphalt mortar can be packaged or stored separately, and not mixed into the room-temperature asphalt liquid temporarily.

[0076] Specifically, the preparation method of the room temperature asphalt mixture in this embodiment is as follows:

[0077] (1) Preparation of filler: Heat the desulfurized gypsum in air at 118°C for 2.5 hours to allow it to react completely. Pass the gypsum through a 0.075mm sieve and collect the undersize portion. Take limestone powder, pass it through a 0.075mm sieve, and collect the undersize portion. Prepare a filler by mixing desulfurized gypsum and limestone powder in a 7:3 mass ratio (corresponding to a 70% desulfurized gypsum content as described below). Dry the filler in an oven at 120°C for 4 hours to remove free and bound water from the desulfurized gypsum and limestone powder.

[0078] (2) Preparation of curing agent: Take commercially available PO42.5 silicate cement (Wuxi Jianghuai Building Materials Science and Technology Co., Ltd.) and ultrafine metakaolin (Shijiazhuang Huabang) and mix them in a mass ratio of 2:1.

[0079] (3) Room temperature asphalt: 55 parts of base asphalt (Donghai brand 90# base asphalt) were heated to 138℃, and 24 parts of reactive liquefaction agent and 14 parts of water-based epoxy resin emulsion (solid content 48%) were added under shear stirring at 50-80 rpm. The mixture was stirred for 15 minutes until it was completely dispersed and uniform to obtain room temperature asphalt. The reactive liquefaction agent was prepared by mixing oleic acid, tetradecyl dimethyl betaine, and tris-(dimethylaminomethyl)phenol polymer in a mass ratio of 10:3:1.

[0080] (4) Preheat the filler to 60℃ and keep it at that temperature for 1 hour. According to the filler to room temperature asphalt mass ratio of 1.05:1, the filler powder is mixed into the room temperature asphalt. The mixture is stirred at 1800 rpm and 60℃ for 15 minutes using a high-speed shearing apparatus, and then stirred at 3000 rpm for 10 minutes to obtain room temperature asphalt liquid.

[0081] (5) Use the following table (Table 1) and Figure 8 The four gradation types of mineral aggregates shown in the median curve were used to prepare room temperature asphalt mixtures. The preparation method was as follows: the mineral aggregates were mixed with the room temperature asphalt liquid prepared in step (4), and stirred evenly at 60°C. Then, a curing agent (accounting for 20 wt.% of the room temperature asphalt) was added, and the mixture was stirred evenly to obtain the room temperature asphalt mixture. The amount of room temperature asphalt in the room temperature asphalt liquid was 5% of the mineral aggregates.

[0082] Table 1:

[0083]

[0084] After the above four groups of ambient temperature asphalt mixtures were laid and shaped, the initial stability, shaping stability, water immersion Marshall stability, flowability, void ratio, aggregate void ratio, asphalt saturation and other indicators were tested. The test results are shown in Table 2 below.

[0085] Table 2:

[0086]

[0087] As observed in the table above, the initial stability of the room-temperature asphalt mixtures in Examples 10-13 is all above 4KN, fully meeting the initial strength requirements for cold-mixed and cold-laid asphalt mixtures for pothole repair in the "Cold-mixed Asphalt Mixtures for Pothole Repair". Among them, the AC-type asphalt mixture exhibits better initial stability and forming stability compared to the SMA-type asphalt mixture with the same nominal maximum particle size. However, in terms of water immersion Marshall stability, the AC-type asphalt mixture is significantly greater than the SMA-type asphalt mixture. This is because although the AC-type asphalt mixture contains more fine aggregate, the desulfurized gypsum in the filler can bond well with the room-temperature liquid asphalt to form a whole. After mixing with the fine aggregate, it forms a high viscosity (tested in Examples 1-5 above), thus enhancing the initial stability of the AC-type asphalt mixture. Although the SMA-type asphalt mixture contains less fine aggregate, the greater number of coarse aggregates interlock to form a stable skeleton structure, and the larger number of fillers forms a "masturbation" with the asphalt, fully filling the gaps between the coarse aggregates. Therefore, the SMA-type asphalt mixture also has high initial stability. However, SMA-type mineral aggregates weaken the volcanic ash effect between inorganic active powder and room temperature asphalt liquid. Furthermore, during immersion in water or when inorganic active powder does not bond well with asphalt, it flows out through the voids under the action of water, resulting in the fact that the immersion Marshall stability of SMA-type asphalt mixtures is not as good as that of AC-type asphalt mixtures.

[0088] Example 14

[0089] The amount of asphalt used significantly impacts the road performance and construction cost of asphalt pavements. Excessive asphalt content can lead to clumping and agglomeration of the mixed material, and also increases the risk of bleeding at high temperatures. Conversely, insufficient asphalt content reduces the viscosity of the asphalt binder or mortar, decreasing the workability and making molding difficult, which negatively affects the durability and water stability of the asphalt pavement. This embodiment uses both empirical formulas and Marshall tests to determine the optimal asphalt content for room-temperature asphalt mixtures using desulfurized gypsum as filler. Specifically, the optimal asphalt content for the selected gradation is determined using an empirical formula from Tongji University, as follows:

[0090] P=0.021a+0.056b+0.099c+0.12d+1.5

[0091] Where: P—optimal bitumen content, %;

[0092] a — Percentage of particles larger than 2.36 mm, in %.

[0093] b—The mass percentage of particles ranging from 0.3 to 2.36 mm, in %.

[0094] C—The mass percentage of particles from 0.075 to 0.3 mm, in % .

[0095] d — the percentage of particles smaller than 0.075 mm, in percentages.

[0096] The mineral aggregate parameters used in the calculation are shown in Table 3 below. The mineral aggregates in the table are selected from the upper and lower limits of AC-16 gradation.

[0097] Table 3:

[0098]

[0099] The optimal bitumen content is calculated to be 5.6 wt.%.

[0100] Example 15

[0101] This embodiment uses the optimal asphalt content (percentage of ambient temperature asphalt to mineral aggregate mass) of 5.6% as the base value, gradually decreasing by 0.5% (4.6%, 5.1%, 5.6%, 6.1%, 6.6%). Marshall tests are used to calculate the stability of various ambient temperature asphalt mixtures. The results are as follows: Figure 9 As shown in the figure. The experimental results are basically consistent with the calculated values, therefore the optimal asphalt content is determined to be 5.6%.

[0102] Example 16

[0103] Select the aggregates shown in Table 3 and determine the asphalt content to be 5.6%. Prepare room temperature asphalt mixtures and obtain molded specimens. The preparation method is the same as steps (1)-(5) of Example 13, except that step (5) is changed to: prepare room temperature asphalt mixtures using mineral aggregates with the gradation shown in Table 3, with an asphalt content of 5.6% of the mineral aggregates. Other treatment methods in step (5) are the same as in Example 13. The room temperature asphalt mixtures are molded into multiple specimens, divided into 7 groups of 4 specimens each. The following indicators are tested and the average of the test values ​​of the 4 specimens is taken:

[0104] ① The initial stability is 5.15 kN, and the molding stability is 15.43 kN.

[0105] With an initial stability of around 5kN, the material fully meets the technical specifications for pothole repair material stability and can also meet the requirement of allowing traffic to resume shortly after pothole repair. The molding stability is greater than 12kN, comparable to hot-mix asphalt mixtures commonly used for pothole repair in the market.

[0106] ②Rutting specimens were prepared in accordance with the test procedure for hot-mix asphalt mixtures and the corresponding tests were conducted. The rutting test results showed that the dynamic stability (cycles / mm) was 4615.

[0107] ③ Prepare low-temperature flexural creep performance test beam specimens according to the operating procedures in the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering". The specifications are 250mm × 30mm × 35mm (length × width × height). Before the test, place the beam specimens in an insulated chamber at -10℃ for 5 hours. Then, apply a uniform load to the middle of the beam specimens in a universal testing machine with an insulated chamber at a loading rate of 50mm / min until the beam specimens bend and fracture. Record the experimental data. The test procedure is as follows: Figure 10 As shown, the performance indicators specified in the low-temperature bending test were calculated. The flexural strength corresponding to the specimen failure process was 3.23 MPa, the maximum flexural tensile strain corresponding to the specimen failure process was 2537.31 με, and the flexural stiffness modulus corresponding to the specimen failure process was 2502.37 MPa. Compared with the low-temperature bending performance indicators of hot-mix asphalt mixtures in the "Technical Specification for Construction of Highway Asphalt Pavement", the room-temperature asphalt mixture molded specimen in this embodiment meets the requirement that the maximum flexural tensile strain (με) is not less than 2500.

[0108] ④ Based on the Marshall immersion test, the Marshall stability of the specimen under immersion is determined as follows:

[0109] The average Marshall stability MS1 value was measured after curing in a constant temperature water tank at 25℃ for 30 minutes: 13.58 kN.

[0110] The average Marshall stability (MS2) was measured after curing in a 25℃ constant temperature water tank for 48 hours: 11.78 kN.

[0111] The residual stability after immersion, MS0 = MS2 / MS1 × 100%, is 86.7%. The residual stability after immersion meets the technical requirement of not less than 85% for residual stability after immersion Marshall test in the "Specifications for Design of Highway Asphalt Pavement".

[0112] ⑤ Referring to the relevant test procedures specified in the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering", the reagents were divided into two groups. One group was cured at room temperature (25℃), and the other group was cured in a freezer at -18℃ for 16 hours after vacuum water sealing treatment. After low-temperature curing, it was then cured in a constant temperature water bath at 60℃ for 24 hours. Subsequently, both groups of specimens were cured together in a constant temperature water bath at 25℃ for 2 hours. The testing instrument used was the SYD-0716 asphalt mixture splitting tensile tester. The average splitting tensile strength RT1 of the specimens without freeze-thaw cycles was 0.85 MPa, and the average splitting tensile strength RT2 of the specimens with freeze-thaw cycles was 0.69 MPa. The freeze-thaw splitting residual strength ratio TSR(%) = RT2 / RT1 × 100%, which was 80.8%. The freeze-thaw splitting residual strength ratio meets the technical standard (freeze-thaw splitting strength ratio of 80%) for the corresponding hot-mix asphalt mixture and annual rainfall greater than or equal to 500 mm, as specified in the "Specifications for Design of Highway Asphalt Pavement" (JTG D50-2017). Furthermore, when the desulfurized gypsum content is 30% and 50% (desulfurized gypsum to limestone powder ratios of 3:7 and 5:5), the freeze-thaw splitting residual strength ratio reaches its peak and second-highest values, respectively.

[0113] ⑥ To investigate the bonding ability between room-temperature asphalt, inorganic powder curing agent, desulfurized gypsum, and aggregates, the cohesiveness test method in the "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40-2004) was used for research and analysis: Approximately 800g of loose room-temperature asphalt mixture was weighed and placed into the corresponding mold, and cured in a 4°C constant temperature curing chamber for 2-3 hours. After curing, the mixture was compacted 5 times on each side using a compactor. The demolded mixture specimen was placed in a standard sieve with a square hole diameter of 26.5mm, and then the specimen was rolled back and forth along the sieve frame 20 times. The average breakage rate was calculated to be 2.52% by weighing the specimen before and after breakage. This breakage rate is far lower than the requirement of less than 40% stipulated in relevant regulations, indicating that the asphalt mixture in this embodiment has very good cohesiveness. Furthermore, when the desulfurized gypsum content is 30% (the ratio of desulfurized gypsum to limestone powder is 3:7), the average breakage rate is 2.30%, which indicates that the cohesiveness and bonding performance of the asphalt mixture at room temperature are greatest when the desulfurized gypsum content is 30%.

[0114] ⑦ Skid Resistance: The surface texture depth of the asphalt mixture containing desulfurized gypsum at room temperature was determined using the sand-spreading method to evaluate the skid resistance of each numbered mixture specimen. The average texture depth of the specimens was 0.972 mm, which is much greater than the requirement of ≥0.55 mm for texture depth TD (annual average rainfall > 1000 mm) specified in the handover inspection index. Furthermore, the texture depth TD values ​​were basically equal when the desulfurized gypsum content was 30% and 50%. This indicates that the asphalt mixture using desulfurized gypsum as filler at room temperature has good skid resistance, and the amount of desulfurized gypsum has little effect on skid resistance.

[0115] Furthermore, the ambient temperature asphalt mixture prepared by the present invention with desulfurized gypsum as filler has good workability. After curing in a refrigerator at -10℃ for 24 hours, no obvious agglomeration or clumping was found. It is easy to mix and has good construction performance. In view of the above performance test results, the ambient temperature asphalt mixture with desulfurized gypsum as filler of the present invention can be used for road pavement construction and pothole repair.

[0116] Furthermore, the ambient temperature asphalt mixture of the present invention can also appropriately incorporate a certain mass ratio of coupling agent, such as a silane coupling agent, preferably a C10-20 alkyltriethoxysilane. This coupling agent can be added to the ambient temperature asphalt liquid prepared in step (4) of Examples 10-13. The ambient temperature asphalt liquid with added coupling agent is then mixed with mineral aggregates of a specific gradation and a curing agent, and stirred evenly to obtain an ambient temperature asphalt mixture containing desulfurized gypsum. It is conceivable that this ambient temperature asphalt mixture will necessarily have better cohesiveness and resistance to high-temperature deformation and low-temperature cracking performance compared to the aforementioned asphalt mixtures.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A room-temperature asphalt mixture using desulfurized gypsum as filler, characterized in that, It includes ambient temperature asphalt mortar and aggregates, wherein the aggregates are AC-16 graded mineral aggregates, and the ambient temperature asphalt in the ambient temperature asphalt mortar accounts for 5.6% of the mass of the mineral aggregates; The ambient temperature asphalt mortar contains fillers, curing agents, and ambient temperature asphalt; the fillers and curing agents are mixed into the ambient temperature asphalt and stirred to obtain the ambient temperature asphalt mortar. The filler is a mixture of desulfurized gypsum and limestone powder, wherein the desulfurized gypsum accounts for 30-70% of the filler mass; the desulfurized gypsum undergoes high-temperature oxidation pretreatment. The mass ratio of filler to room temperature asphalt is 0.8-1.1:1; The curing agent is a mixture of silicate cement and metakaolin, and the amount of curing agent used is 15-25% of the mass of the asphalt at room temperature; The pretreatment method for desulfurized gypsum is as follows: the desulfurized gypsum is heated in an air atmosphere at 115-124℃ and reacted fully for more than 2 hours; the filler preparation method is as follows: the pretreated desulfurized gypsum and limestone powder are passed through a 0.075mm sieve and the undersize portion is taken, and then treated in an oven at 120-124℃ for more than 3 hours to remove free water and bound water from the desulfurized gypsum and limestone powder; the room temperature asphalt is a reactive room temperature liquid asphalt, which is prepared by adding a reactive liquefying agent and a modifier waterborne epoxy resin emulsion to a fluid matrix asphalt and then shearing and mixing it; wherein, the reactive liquefying agent is prepared by adding unsaturated fatty acids as the liquefying agent matrix material, adding zwitterionic surfactants and phenol polymers and stirring and mixing.

2. The ambient temperature asphalt mixture using desulfurized gypsum as filler according to claim 1, characterized in that, The desulfurized gypsum has a mass fraction of 30% or 70% in the filler.

3. The ambient temperature asphalt mixture using desulfurized gypsum as filler according to claim 1, characterized in that, The mass ratio of the filler to room temperature asphalt is 1:1; the mass ratio of silicate cement to metakaolin in the curing agent is 2:

1.

4. The ambient temperature asphalt mixture using desulfurized gypsum as filler according to claim 1, characterized in that, The amount of curing agent is 19-21% of the mass of asphalt at room temperature.

5. The ambient temperature asphalt mixture using desulfurized gypsum as filler according to claim 1, characterized in that, The reactive room-temperature liquid asphalt is prepared by adding 20-30 parts by weight of reactive liquefaction agent and 10-20 parts by weight of water-based epoxy resin emulsion modifier to 50-60 parts by weight of base asphalt that has been heated to a fluid state at high temperature, and then mixing it by shearing and stirring. The reactive liquefaction agent is prepared by mixing unsaturated fatty acids as the liquefaction agent matrix material with alkyl dimethyl betaine and phenol polymer; wherein the mass ratio of unsaturated fatty acids:alkyl dimethyl betaine:phenol polymer is 15-25:5-10:1-5; the unsaturated fatty acids are at least one of myristoleic acid, trans oleic acid, oleic acid, linoleic acid, erucic acid, palmitoleic acid, and ricinoleic acid; the alkyl dimethyl betaine is C10-20 alkyl dimethyl betaine; and the phenol polymer is tris-(dimethylaminomethyl)phenol polymer.

6. The ambient temperature asphalt mixture using desulfurized gypsum as filler according to claim 1 or 5, characterized in that, The reactive room-temperature liquid asphalt also contains 10-20 parts by weight of coupling agent.

Images