Basalt fiber reinforced coal gangue asphalt mixture, preparation method and application thereof

Abstract

The present application relates to the field of road engineering materials and solid waste resource utilization technology, and particularly relates to basalt fiber reinforced coal gangue asphalt mixture and a preparation method and application thereof, which comprises, by weight, activated coal gangue aggregate 100 parts, asphalt binder 4-7 parts, basalt fiber 0.2-0.5 parts, slaked lime 1-3 parts and silane coupling component 0.3-1.5 parts. The coal gangue is calcined at 550-850 DEG C to remove hydroxyl groups, and the surface is converted into a slightly alkaline amorphous silicon aluminum active surface; the silicon aluminum homology of the coal gangue and the basalt fiber is utilized, and the aggregate and the fiber are covalently bonded into a continuous stress aggregate-fiber-asphalt interface network through Si--O--Si and Si--O--Al at the contact interface by using the same silane coupling system; the slaked lime has the triple effects of anti-peeling, alkaline activation and calcium node, and the freeze-thaw splitting strength ratio is more than 90% and the dynamic stability is more than 6000 times / mm while realizing the solid waste resource utilization.

Description

Technical Field

[0001] This invention relates to the field of road engineering materials and solid waste resource utilization technology, specifically to basalt fiber reinforced coal gangue asphalt mixture, its preparation method and application. Background Technology

[0002] Asphalt pavement is the main structural form of highways and urban roads of all grades, and its performance largely depends on the interfacial adhesion between the aggregate and the asphalt. Coal gangue is a solid waste discharged during coal mining and washing. Long-term stockpiling of coal gangue occupies land and pollutes the environment. Crushing and grading it for use as aggregate in asphalt mixtures is an important way to realize the resource utilization of solid waste. However, coal gangue is mainly composed of aluminosilicate minerals such as kaolinite, illite, and quartz. Its original surface is acidic and porous, containing adsorbed water, resulting in poor adhesion to asphalt and weak resistance to water damage. When used directly as aggregate, the water stability of the asphalt mixture is difficult to meet the specifications.

[0003] To improve the crack resistance and deformation resistance of asphalt mixtures, existing technologies often incorporate fibers for reinforcement. Chinese patent CN107445518A discloses a high-fatigue-resistant graded basalt fiber asphalt mixture and its preparation method. This mixture uses SBS-modified asphalt, graded basalt fibers, and aggregates to improve the fatigue crack resistance of asphalt pavements by utilizing the reinforcing effect of basalt fibers. However, in this technology, the basalt fibers are only physically dispersed in the asphalt mastic. The fiber surface is smooth, and the interaction with the asphalt is purely physical adsorption. Under repeated loading and the coupling effect of water, the fibers are easily pulled out of the asphalt matrix, resulting in a short-lasting reinforcement effect. Furthermore, this technology uses conventional aggregates and does not address the issue of solid waste resource utilization.

[0004] Patent CN116675501B discloses an early-strength, freeze-thaw resistant cold-patch asphalt mixture and its construction method. The mixture contains asphalt, cement, basalt fiber, quicklime, and hyperbranched epoxy resin, achieving early strength and freeze-thaw resistance through the curing of the epoxy resin. However, the strength of this technology originates from the organic curing system of the epoxy resin. Quicklime is only a conventional component, and no chemical bond is established between the basalt fiber and the aggregate. Furthermore, it is designed for the specific scenario of cold-patch curing and does not address the interfacial integration between coal gangue aggregate and fiber.

[0005] To address the water stability issue at the aggregate-asphalt interface, invention patent CN110760258B discloses an asphalt interface modifier, its preparation method, and its application. This modifier forms a resin film by spraying it onto the aggregate surface, transforming the aggregate-asphalt two-phase interface into an aggregate-modifier-asphalt three-phase interface. The patent explicitly points out that existing anti-stripping methods, from inorganic slaked lime to organic anti-stripping agents, and from asphalt modification to aggregate modification, only alleviate water damage to a certain extent without achieving a breakthrough in the underlying mechanism. Alkaline substances such as slaked lime only undergo physical adsorption on acidic aggregate surfaces, resulting in poor long-term effectiveness. However, this patent modifies inert aggregates using a resin film spraying method, which suffers from high material costs, complex processes, and difficulty in ensuring uniformity. Furthermore, it does not utilize the chemical activity of the aggregate surface itself, nor does it integrate fibers and aggregates into a continuously stressed interface through the same chemical system.

[0006] Furthermore, existing research indicates that high-temperature calcination of coal gangue can dehydroxylate kaolinite, transforming it into a highly active metakaolinite phase. The optimal activation temperature is typically between 700 and 850°C; excessively high temperatures can lead to the formation of mullite, thus reducing its activity. Current technologies often utilize activated coal gangue as a pozzolanic admixture in cement-based materials, leveraging its activity to participate in hydration reactions and generate hydration products. However, in asphalt mixtures, a system devoid of hydration reactions, the art generally considers there to be a lack of clear motivation for calcining and activating coal gangue used as aggregate. Consequently, the interfacial coupling value of activated coal gangue surfaces in asphalt systems has long been unrecognized and unutilized.

[0007] In summary, existing technologies have the following shortcomings: First, coal gangue aggregates have an acidic and inert surface, poor adhesion to asphalt, and weak resistance to water damage; second, basalt fibers and asphalt are only physically blended, making them easily pull-out under load, and the aggregates and fibers are considered as two unrelated phases, lacking a means to chemically integrate them into a continuous stress-bearing interface; third, hydrated lime only undergoes physical adsorption on the surface of inert acidic aggregates, with limited effect. Therefore, how to achieve the resource utilization of coal gangue solid waste while simultaneously bonding coal gangue aggregates and basalt fibers into a continuous stress-bearing interface network through the same chemical system, thereby fundamentally improving the water stability and overall road performance of asphalt mixtures, is a technical problem urgently needing to be solved in this field.

[0008] The large-scale utilization of coal gangue has always been a challenge in the field of solid waste treatment. The annual stockpiling volume of coal gangue is enormous, and its annual emissions continue to increase. This stockpiling not only occupies a large amount of land but also poses a risk of air and water pollution due to spontaneous combustion and leaching. Using coal gangue in road construction is an effective way to achieve large-scale disposal, but using it as an aggregate in asphalt mixtures faces two inherent obstacles: First, the strength and abrasion resistance of coal gangue are generally lower than that of high-quality crushed stone, and its porous, water- and oil-absorbing properties lead to a high asphalt-aggregate ratio and reduced economic efficiency in the mixture. Second, the surface of the aluminosilicate minerals in the main body of coal gangue is electronegative and hydrophilic and oleophobic, lacking effective chemical bonding with the similarly acidic asphalt. The interface relies mainly on physical adsorption, and under repeated water action, the asphalt film easily peels off from the aggregate surface, causing water damage such as particle shedding, loosening, and potholes. Water damage to asphalt pavements is essentially a process in which water molecules compete with asphalt and aggregates for adsorption, gradually displace, and weaken the interfacial bond at the aggregate-asphalt interface. Therefore, improving the chemical bonding at the aggregate-asphalt interface and blocking the intrusion path of water molecules are key to fundamentally improving the water stability and durability of asphalt pavements. Although existing technologies have proposed many solutions for aggregate modification, fiber reinforcement, and anti-stripping agents, none of them have combined the surface chemical activation of coal gangue aggregates with the chemical integration of the aggregate-fiber-asphalt three-phase system, nor have they recognized that the silicon-aluminum homology of coal gangue and basalt fibers can be utilized by the same coupling system. Summary of the Invention

[0009] To address the aforementioned technical problems, the present invention aims to provide basalt fiber reinforced coal gangue asphalt mixture, its preparation method, and its applications. This invention utilizes the homology of coal gangue and basalt fiber as both being silica-alumina compounds, using the same silane coupling system to bond calcined and activated coal gangue aggregate and basalt fiber into a continuously stressed aggregate-fiber-asphalt interface network. This achieves resource utilization of solid waste while significantly improving the water stability, high-temperature rutting resistance, and low-temperature crack resistance of the asphalt mixture.

[0010] To achieve the above objectives, this invention provides a basalt fiber reinforced coal gangue pitch mixture, comprising, by weight, 100 parts activated coal gangue aggregate, 4-7 parts pitch binder, 0.2-0.5 parts basalt fiber, 1-3 parts hydrated lime, and 0.3-1.5 parts silane coupling component. The activated coal gangue aggregate is coal gangue particles calcined at a controlled temperature of 550-850°C to remove hydroxyl groups. Calcination removes residual carbon and adsorbed water from its surface, transforming the surface kaolinite into a slightly alkaline amorphous silicon-aluminum phase, thereby converting the originally acidic and inert surface into a slightly alkaline active surface exposing silicon-oxygen and aluminum-oxygen active sites. The silane coupling component contains hydrolyzable trialkoxysilane groups, which, after hydrolysis, condense with the silanol groups on the surface of the activated coal gangue aggregate and the basalt fiber to form Si—O—Si and Si—O—Al covalent bonds. Since activated coal gangue aggregate and basalt fiber are both silica-alumina and have the same surface chemistry, the same silane coupling system can bond the two at the same time, so that the aggregate and fiber are connected to each other through covalent bonds at their contact interface and connected to the asphalt through the coupling layer, thus forming a continuously stressed aggregate-fiber-asphalt interface network.

[0011] Further, the silane coupling component includes one or more of the following: a dual-anchor bridging silane coupling agent, an asphaltene-anchored silane coupling agent, and a calcium chelate bridging silane coupling agent. The dual-anchor bridging silane coupling agent has a hydrolyzable trialkoxysilane group at each end, which condenses with silanol groups on the surfaces of activated coal gangue aggregates and basalt fibers, respectively, forming a direct covalent bridge between the aggregates and fibers. The asphaltene-anchored silane coupling agent has a hydrolyzable trialkoxysilane group at one end and an asphaltene affinity group containing a thiophene ring at the other end. The thiophene ring is embedded in the asphaltene aggregate via π-π stacking and coordination with sulfur atoms, anchoring the asphalt phase into the inorganic network. The calcium chelate bridging silane coupling agent simultaneously has two hydrolyzable trialkoxysilane groups and one β-dicarbonyl chelating group. The β-dicarbonyl chelating group chelates calcium ions released from slaked lime, transforming the slaked lime from physical adsorption into a chemically bonded bridging node in the interfacial network.

[0012] As a preferred embodiment of the present invention, the calcination activation temperature of the coal gangue is 650~800°C and the calcination time is 1~3 h, so as to fully dehydroxylate and generate amorphous metakaolinite phase while avoiding the formation of mullite; in the silane coupling component, the weight ratio of the dual-anchor bridging silane coupling agent, the asphalt-anchoring silane coupling agent and the calcium chelating bridging silane coupling agent is (2~4):(1~2):(1~2), so as to take into account the synergy of aggregate-fiber bridging, asphalt phase anchoring and calcium node crosslinking; the diameter of the basalt fiber is 7~15 μm and the length is 3~9 mm, so as to ensure the dispersion and reinforcement effect of the fiber in the asphalt mortar; the amount of mineral powder is 3~8 parts by weight. As a further preferred embodiment of the present invention, the silane coupling component contains the above three coupling agents, so that the direct bridging between aggregate and fiber, the active anchoring of the asphalt phase and the calcium node formation of hydrated lime are synergistically achieved in the same system, thereby obtaining the optimal water stability and comprehensive road performance.

[0013] The beneficial effects of this invention are as follows: First, coal gangue solid waste is used as aggregate in asphalt mixtures. Calcination and activation transform its surface defects into interfacial coupling advantages, realizing the resource utilization of solid waste and carbon reduction. Second, by utilizing the silicon-aluminum homology of aggregates and fibers, the two are bonded into a continuously stressed interfacial network through the same coupling system, which significantly improves aggregate-asphalt adhesion and water stability. The fibers are transformed from physical dispersion to chemical anchoring, making them less prone to pull-out, and the high-temperature rutting resistance and fatigue resistance are improved simultaneously. Third, the pores of the activated aggregate are pre-sealed by the coupling component, which reduces the absorption of free asphalt while providing mechanical interlocking, thereby reducing the optimal asphalt-aggregate ratio and achieving cost reduction, carbon reduction, and rutting resistance. Fourth, quicklime has a triple effect of anti-stripping, alkaline activation, and calcium node formation, which addresses the shortcomings of the existing technology where quicklime only physically adsorbs. Tests show that the freeze-thaw splitting strength ratio of the asphalt mixture of this invention can reach over 90%, the residual stability after immersion in water can reach over 94%, the dynamic stability can reach over 6000 times / mm, and the water stability even exceeds that of the conventional limestone or basalt crushed stone control group, achieving the goal of replacing high-quality aggregates with solid waste without reducing performance but rather increasing it. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the method for preparing basalt fiber reinforced coal gangue asphalt mixture according to the present invention;

[0015] Figure 2 This is a schematic diagram of the microstructure of the aggregate-fiber-asphalt three-phase transition layer of the present invention;

[0016] Figure 3 This is a comparison chart of the freeze-thaw splitting strength ratio, dynamic stability, and low-temperature bending failure strain performance of the embodiments and comparative examples of the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto.

[0018] The raw materials used in each embodiment of this invention are as follows: Coal gangue is obtained from coal mine washing waste. Its main chemical composition, by mass, is SiO2 52.3%, Al2O3 28.6%, Fe2O3 5.2%, and loss on ignition 8.7%. The main minerals are kaolinite and quartz. It is crushed and graded into coarse aggregate with a particle size of 4.75~13.2 mm and fine aggregate with a particle size of 0~4.75 mm for later use. Basalt fiber is short-cut fiber with a diameter of 10~15 μm, a length of 6 mm, a tensile strength greater than 3000 MPa, and an elastic modulus greater than 90 GPa. The asphalt binder uses SBS modified asphalt with a penetration of 70 and a softening point of 78°C. The hydrated lime is industrial-grade calcium hydroxide Ca(OH)2 with a purity greater than 90%. The mineral powder is limestone mineral powder with a particle size less than 0.075 mm. Figure 1 As shown, the preparation process of the present invention includes the following steps in sequence: calcination and activation of coal gangue, pre-coating and pore sealing of activated aggregate surface, surface modification of basalt fiber, dry mixing and hot-mix curing of sprayed asphalt.

[0019] The coal gangue has a chemical composition of over 80% SiO2 and Al2O3, making it a typical aluminosilicate material. This is the basis for the present invention's ability to utilize its homology with basalt fiber for co-coupling. Basalt fiber is made by high-temperature melting and drawing of natural basalt, and its main components are also aluminosilicate glass, such as SiO2, Al2O3, CaO, MgO, and iron oxides. Its surface can expose silanol reaction sites after alkali etching or silane treatment, thus the two can be bonded by the same silane coupling system. The calcination equipment uses a box-type resistance furnace or rotary kiln, with the heating rate controlled at 5~10°C / min. After constant-temperature calcination, it is cooled with the furnace or naturally cooled to room temperature for later use.

[0020] The silane coupling components used in this invention include one or more of the following three coupling agents, and their preparation methods are as follows. The dual-anchored bridging silane coupling agent is 3-(4,4-diethoxy-9-oxayne-8-aza-3-oxa-4-silanon-9-yl)-N-(4,4-diethoxy-3-oxa-4-silanoheptane-7-yl)-5-(dodecyloxy)benzamide, which is prepared by Williamson etherification and saponification of dimethyl-5-hydroxyisophthalate and 1-bromododecane to obtain 5-(dodecyloxy)isophthalic acid, followed by thionyl chloride chlorination and amidation with 3-aminopropyltriethoxysilane. Its molecule has a triethoxysilyl group at each end and a long dodecyloxy chain in the central benzene ring. The asphaltene-anchored silane coupling agent is N-(4,4-diethoxy-3-oxa-4-silazept-7-yl)-5-octylthiophene-2-carboxamide, prepared by acylation of 5-octylthiophene-2-carboxylic acid followed by amidation with 3-aminopropyltriethoxysilane, with one end being a triethoxysilyl group and the other end being an octylthiophene ring. The calcium chelate-bridged silane coupling agent is 2-(4,4-diethoxy-9-oxylidene-8-aza-3-oxa-4-silazonon-9-yl)-N-(4,4-diethoxy-3-oxa-4-silazept-7-yl)-3-oxylidenebutyramide, prepared by diester ammonolysis of diethyl 2-acetylmalonate and 3-aminopropyltriethoxysilane, with a β-dicarbonyl chelate structure composed of an acetyl group and an amide at the center of the molecule and a triethoxysilyl group at each end. After hydrolysis, the silanol groups at both ends of the double-anchored bridging silane coupling agent condense with the surfaces of activated coal gangue aggregate and basalt fiber, respectively, forming a molecular bridge between them.

[0021] To fully disclose the preparation of the above three novel coupling agents, detailed preparation examples are given below.

[0022] Preparation Example 1

[0023] Preparation of 3-(4,4-diethoxy-9-oxayne-8-aza-3-oxa-4-silane-non-9-yl)-N-(4,4-diethoxy-3-oxa-4-silane-hept-7-yl)-5-(dodecyloxy)benzamide:

[0024] Step 1, Etherification: In a three-necked flask equipped with a stirrer and a reflux condenser, 21.0 g (0.10 mol) of dimethyl-5-hydroxyisophthalate, 27.4 g (0.11 mol) of 1-bromododecane, 20.7 g (0.15 mol) of anhydrous potassium carbonate, 1.0 g of potassium iodide, and 150 mL of N,N-dimethylformamide were added. The mixture was stirred at 80°C for 12 h. After cooling, the mixture was poured into 500 mL of ice water, and a solid precipitated. The solid was filtered, washed with water, and recrystallized from anhydrous ethanol to give 34.1 g of white solid dimethyl-5-(dodecyloxy)isophthalate, with a yield of 90%.

[0025] Step 2, Saponification: 30.4 g (80 mmol) of the above-mentioned dimethyl-5-(dodecyloxy)isophthalic acid ester was dissolved in 120 mL of a mixed solvent of tetrahydrofuran and methanol. An alkaline solution prepared by dissolving 9.6 g of sodium hydroxide in 40 mL of water was added, and the mixture was refluxed and stirred at 65°C for 4 h. After removing the organic solvent under reduced pressure, the pH was adjusted to 2 with 2 mol / L hydrochloric acid, precipitating a white solid. The solid was filtered, washed with water until neutral, and dried to obtain 26.8 g of 5-(dodecyloxy)isophthalic acid, with a yield of 95%.

[0026] Step 3, Acyl chloride and amidation: 17.5 g (50 mmol) of 5-(dodecyloxy)isophthalic acid was mixed with 40 mL of thionyl chloride, and 2 drops of N,N-dimethylformamide were added dropwise as a catalyst. The mixture was refluxed at 75°C and stirred for 3 h until the solid was completely dissolved. Excess thionyl chloride was removed by vacuum distillation to obtain 5-(dodecyloxy)isophthaloyl chloride, which was dissolved in 30 mL of anhydrous dichloromethane. Under nitrogen protection, the acyl chloride solution was slowly added dropwise to a 100 mL dichloromethane solution pre-cooled to 0°C containing 23.2 g (0.105 mol) of 3-aminopropyltriethoxysilane and 11.1 g (0.11 mol) of triethylamine. After the addition was complete, the mixture was brought to room temperature and stirred for 6 h. Triethylamine hydrochloride was removed by filtration. The filtrate was washed successively with saturated sodium bicarbonate solution and saturated brine, dried over anhydrous sodium sulfate, and desolventized under reduced pressure to obtain a pale yellow viscous liquid, namely 32.2 g of 3-(4,4-diethoxy-9-oxayne-8-aza-3-oxa-4-silane-non-9-yl)-N-(4,4-diethoxy-3-oxa-4-silane-heptane-7-yl)-5-(dodecyloxy)benzamide, with a yield of 85%.

[0027] The structure of 3-(4,4-diethoxy-9-oxayne-8-aza-3-oxa-4-silane-non-9-yl)-N-(4,4-diethoxy-3-oxa-4-silane-hept-7-yl)-5-(dodecyloxy)benzamide was confirmed: 1H NMR (400 MHz, CDCl3) δ: 7.86 (s, 1H, ArH-2), 7.38 (s, 2H, ArH-4,6), 6.55 (br, 2H, 2×NH), 4.01 (t, J=6.6Hz, 2H, OCH2), 3.82 (q, J=7.0 Hz, 12H, SiOCH2), 3.45 (q, 4H, NHCH2), 1.80 (m, 4H, NHCH2CH2), 1.77 (m, 2H, OCH2CH2), 1.45~1.26 (m, 18H, (CH2)9), 1.22 (t, J=7.0 Hz, 18H, OCH2CH3), 0.88 (t, 3H, CH3), 0.66 (m, 4H, SiCH2); 13 C NMR (100 MHz, CDCl3) δ: 166.6, 159.6, 135.9, 117.0, 115.8, 68.4, 58.5, 42.1, 31.9, 29.6, 25.9, 23.3, 18.3, 14.1, 7.8; IR (KBr, cm -1 ): 3305 (N—H), 2925, 2854, 1640 (amide I), 1540 (amide II), 1100, 1080 (Si—O—C), 955 (Si—O); ESI-MS m / z: 757.49 ([M+H]) + ), 779.47([M+Na] + ); Elemental analysis (C 38 H 72 The theoretical values ​​for N2O9Si2 are C 60.28, H 9.59, and N 3.70, while the measured values ​​are C 60.15, H 9.66, and N 3.62.

[0028] Preparation Example 2

[0029] Preparation of N-(4,4-diethoxy-3-oxa-4-silazopent-7-yl)-5-octylthiophene-2-carboxamide:

[0030] Step 1, Precursor Preparation and Acyl Chlorination: 5-Octylthiophene-2-carboxylic acid can be prepared by coupling 5-bromothiophene-2-carboxylic acid with n-octylmagnesium bromide via Kumada, or by lithiation of 2-octylthiophene with n-butyllithium followed by carboxylation with carbon dioxide. Mix 12.0 g (50 mmol) of 5-octylthiophene-2-carboxylic acid with 30 mL of thionyl chloride, add 2 drops of N,N-dimethylformamide, reflux and stir at 75°C for 3 h, remove excess thionyl chloride under reduced pressure to obtain 5-octylthiophene-2-carboxyl chloride, which is then dissolved in 30 mL of anhydrous dichloromethane for later use.

[0031] Step 2, amidation: Under nitrogen protection, the above 5-octylthiophene-2-carboxyl chloride solution was slowly added dropwise to an 80 mL dichloromethane solution pre-cooled to 0°C containing 11.6 g (52.5 mmol) of 3-aminopropyltriethoxysilane and 5.6 g (55 mmol) of triethylamine. After the addition was complete, the mixture was brought to room temperature and stirred for 6 h. The triethylamine hydrochloride was removed by filtration. The filtrate was washed successively with saturated sodium bicarbonate solution and saturated brine, dried over anhydrous sodium sulfate, desolventized under reduced pressure, and purified by short silica gel column chromatography to obtain a pale yellow liquid, namely 19.5 g of N-(4,4-diethoxy-3-oxa-4-silazepen-7-yl)-5-octylthiophene-2-carboxamide, with a yield of 88%.

[0032] Structure confirmation of N-(4,4-diethoxy-3-oxa-4-silazepept-7-yl)-5-octylthiophene-2-carboxamide: 1 ¹H NMR (400 MHz, CDCl₃) δ: 7.30 (d, J = 3.8 Hz, 1H, thiophene H⁻³), 6.75 (d, J = 3.8 Hz, 1H, thiophene H⁻⁴), 6.10 (br, 1H, NH), 3.82 (q, J = 7.0 Hz, 6H, SiOCH₂), 3.40 (q, 2H, NHCH₂), 2.82 (t, J = 7.5 Hz, 2H, thiophene CH₂), 1.75 (m, 2H, NHCH₂CH₂), 1.66 (m, 2H, CH₂), 1.35–1.25 (m, 10H, (CH₂)₅), 1.22 (t, J = 7.0 Hz, 1H, (CH₂)₅). Hz, 9H, OCH2CH3), 0.88 (t, 3H, CH3), 0.64 (m, 2H, SiCH2); 13 C NMR (100 MHz, CDCl3) δ: 161.8, 152.0, 138.5, 128.0, 124.5, 58.4, 42.0, 31.8, 30.2, 29.2, 22.6, 18.3, 14.1, 7.7; IR (KBr, cm -1 ): 3320 (N—H), 2925, 2855, 1625 (amide I), 1540 (amide II), 1080 (Si—O—C), 800 (thiophene ring); ESI-MS m / z: 444.26 ([M+H] + ), 466.24([M+Na] + ); Elemental analysis (C 22 H 41 The theoretical values ​​of NO4SSi are C 59.55, H 9.31, N 3.16, S 7.23, and the measured values ​​are C 59.42, H 9.39, N 3.10, S 7.15.

[0033] Preparation Example 3

[0034] Preparation of 2-(4,4-diethoxy-9-oxylidene-8-aza-3-oxa-4-silanenon-9-yl)-N-(4,4-diethoxy-3-oxa-4-silaneheptane-7-yl)-3-oxylidenebutyramide:

[0035] Diester ammonolysis: In a three-necked flask equipped with a stirrer, thermometer, and distillation apparatus, 10.1 g (50 mmol) of diethyl 2-acetylmalonate and 50 mL of anhydrous toluene were added. Under nitrogen protection, 23.2 g (0.105 mol) of 3-aminopropyltriethoxysilane was slowly added dropwise at 0°C. After the addition was complete, the temperature was slowly raised to 70°C and the mixture was stirred for 10 h. During the reaction, the generated ethanol was continuously distilled off to promote the ammonolysis equilibrium. After the reaction was complete, toluene and residual ethanol were removed under reduced pressure. The crude product was purified by short silica gel column chromatography to obtain a colorless to pale yellow viscous liquid, namely 22.1 g of 2-(4,4-diethoxy-9-oxylidene-8-aza-3-oxa-4-silanenon-9-yl)-N-(4,4-diethoxy-3-oxa-4-silaneheptane-7-yl)-3-oxylidenebutyramide, with a yield of 80%. To suppress the side reaction of acetyl reacting with amine to form enamine, the dropping rate was controlled and the reaction temperature was kept below 70°C. The central acetyl group of this compound forms a β-dicarbonyl structure with the amide, and it exhibits keto-enol tautomerism in solution. The enol form is the active configuration that chelates calcium ions.

[0036] The structure of 2-(4,4-diethoxy-9-oxoylide-8-aza-3-oxa-4-silanenon-9-yl)-N-(4,4-diethoxy-3-oxa-4-silanehept-7-yl)-3-oxoylide-butyramide was confirmed (primarily in keto form): 1 ¹H NMR (400 MHz, CDCl₃) δ: 7.45 (br, 2H, 2×NH), 4.66 (s, 1H, COCH(CO)₂), 3.82 (q, J=7.0 Hz, 12H, SiOCH₂), 3.30 (q, 4H, NHCH₂), 2.35 (s, 3H, COCH₃), 1.65 (m, 4H, NHCH₂CH₂), 1.22 (t, J=7.0 Hz, 18H, OCH₂CH₃), 0.62 (m, 4H, SiCH₂), enol form visible δ approximately 13.5 (br, enol OH); 13 C10 NMR (100 MHz, CDCl3) δ: 202.5 (ketone carbonyl), 165.8 (amide carbonyl), 64.5 (methylbenzene), 58.5, 41.8, 29.5, 22.6, 18.3, 7.6; IR (KBr, cm⁻¹) -1): 3290 (N—H), 2975, 2930, 1715 (ketone carbonyl), 1660 (amide I), 1540 (amide II), 1080 (Si—O—C); ESI-MS m / z: 553.30 ([M+H] + ), 575.28([M+Na] + ); Elemental analysis (C 23 H 48 The theoretical values ​​of N2O9Si2 are C 49.97, H 8.75, N 5.07, and the measured values ​​are C 49.85, H 8.83, N 4.99.

[0037] Example 1

[0038] This embodiment provides a basalt fiber reinforced coal gangue pitch mixture, the preparation process of which is as follows. First, activated coal gangue aggregate is prepared by placing the graded coal gangue in a calcining furnace and calcining it at 750°C for 2 hours under controlled temperature. This process removes residual carbon and adsorbed water from the surface, and dehydroxylates the surface kaolinite, transforming it into a slightly alkaline amorphous metakaolinite phase, thus obtaining activated coal gangue aggregate. Measurements show that its specific surface area increases from 3.1 m² before activation. 2 / g increased to 8.4 m 2 / g, the surface pH increased from 6.2 to 9.1, and the open porosity increased from 4.2% before activation to 6.8%, indicating that activation cleans and opens pores while changing the surface from slightly acidic and inert to slightly alkaline and active.

[0039] Subsequently, surface coupling pre-coating and pore sealing of the activated aggregate were performed. According to the proportions in this embodiment, the total amount of silane coupling components was 0.9 parts by weight, including 0.40 parts of double-anchored bridging silane coupling agent, 0.25 parts of asphalt-based anchoring silane coupling agent, and 0.25 parts of calcium-chelated bridging silane coupling agent. The three coupling agents were dissolved in anhydrous ethanol and a small amount of water was added to prepare a hydrolysate. The pH was adjusted to 4.5 to moderately hydrolyze the trialkoxysilane groups. The hydrolysate was then sprayed onto the surface of 100 parts by weight of activated coal gangue aggregate, and 0.5 parts of slaked lime was added to provide an alkaline environment to activate the condensation of silanol groups. The mixture was stirred and mixed at 60°C for 30 min, allowing the coupling agent to penetrate into the open pores and condense into a film at the pore openings and on the surface. This not only sealed the pores but also constructed a coupling layer on the aggregate surface that could bond with fibers and asphalt, resulting in coupling-modified activated coal gangue aggregate.

[0040] Next, the surface modification of the basalt fiber was carried out. 0.35 parts by weight of basalt fiber were etched with a 3% sodium hydroxide solution, washed with water, and dried. Then, it was impregnated with an ethanol hydrolysate of a dual-anchor bridging silane coupling agent to expose the fiber surface and graft silanol groups, thus obtaining modified basalt fiber. Then, dry mixing was carried out. The above-mentioned coupling-modified activated coal gangue aggregate, modified basalt fiber, 1.5 parts of the remaining hydrated lime, and 5 parts of limestone powder were dry mixed at 160°C for 90 s to ensure uniform distribution of the components.

[0041] Finally, heated asphalt binder is sprayed in and hot-mixed. 5.5 parts by weight of SBS modified asphalt with a penetration of 70, heated to 165°C, is sprayed into the above dry-mixed material according to the asphalt-aggregate ratio, and hot-mixed at 165°C for 120 seconds. During the hot-mixing process, the silane coupling components grafted onto the activated aggregate surface and fiber surface further condense and solidify. The double-anchored bridging silane coupling agent forms Si-O-Si and Si-O-Al covalent bridges at the interface between the aggregate and fiber. The thiophene ring of the asphaltene anchoring silane coupling agent is embedded in the asphaltene aggregate. The β-dicarbonyl group of the calcium chelate bridging silane coupling agent chelates calcium ions released from slaked lime to form calcium bridging nodes, such as... Figure 2 and Figure 3 As shown, the aggregate, fiber, and asphalt thus form a continuously stressed interfacial symbiotic network. The resulting mixture was subjected to Marshall compaction molding and testing, and the optimal asphalt-aggregate ratio for this embodiment was determined to be 5.0%.

[0042] To characterize the formation of the interfacial symbiotic network in this embodiment, microscopic analysis was performed on the coal gangue before and after activation and the resulting mixture. X-ray diffraction analysis showed that before activation, the coal gangue exhibited characteristic kaolinite diffraction peaks at 2θ of 12.4° and 24.9°. After activation at 750°C, these characteristic kaolinite peaks largely disappeared, replaced by broadened amorphous diffuse peaks, indicating that the kaolinite had undergone dehydroxylation and transformed into an amorphous meta-kaolinite phase, and no sharp mullite diffraction peaks appeared. Fourier transform infrared spectroscopy analysis showed that after activation, the 3690 cm⁻¹ peak corresponding to the hydroxyl groups on the kaolinite surface... -1 With 3620 cm -1 The absorption peaks were significantly weakened, and the vibrational peaks of the Si—O—Si and Si—O—Al frameworks shifted, confirming the reconstruction of surface hydroxyl groups and the rearrangement of the silicon-aluminum framework; after treatment with silane coupling components, the absorption peaks at 2900 cm⁻¹ were observed. -1 A methylene stretching vibration peak appears nearby at 1650 cm⁻¹. -1 The presence of amide carbonyl vibration peaks nearby indicates that the coupling agent has been grafted onto the aggregate surface. Scanning electron microscopy observation shows that the activated coal gangue aggregate surface has cleaner pores and increased roughness. After coupling treatment and hot mixing, a continuous transition layer is visible between the aggregate and basalt fibers. The fibers are firmly wrapped by the asphalt mastic and coupling layer rather than being isolated and suspended. Figure 3The three-phase transition layer structures shown are consistent. Energy dispersive spectroscopy analysis indicates that the distribution of silicon, aluminum, and calcium elements in the aggregate-fiber interface region is continuous, corroborating the continuous interface network formed by Si-O-Si and Si-O-Al covalent bonds and calcium chelate nodes.

[0043] In the gradation design of this embodiment, the activated coal gangue coarse aggregate, fine aggregate, and mineral powder are composed of AC-13 continuous dense gradation. The aggregate gradation meets the standard gradation range, with a 4.75 mm sieve passing rate of 45%, a 2.36 mm sieve passing rate of 32%, and a 0.075 mm sieve passing rate of 6%. Marshall compaction tests were conducted using standard specimens formed by compacting each side 75 times. The measured bulk relative density of the mixture in this embodiment was 2.41, the porosity was 4.1%, the aggregate void ratio was 14.2%, and the asphalt saturation was 71%. All volumetric indicators meet the design requirements for heavy-duty traffic asphalt pavement, indicating that this invention maintains good mixture volume stability and workability while improving interfacial performance.

[0044] To illustrate the synergistic effect of the three coupling agents in this embodiment, a comparative observation was conducted on systems containing only a single coupling agent. When the coupling component contained only a dual-anchor bridging silane coupling agent, although bridging was formed between the aggregate and the fiber, the bond between the bridging zone and the asphalt was weak, and the water-immersion residual stability of the mixture decreased compared to the three-agent synergistic system. When the coupling component contained only an asphaltene-anchoring silane coupling agent, although the asphalt phase was anchored, there was a lack of direct bridging between the aggregate and the fiber, limiting the reinforcing effect of the fiber. When the coupling component contained only a calcium-chelating bridging silane coupling agent, the quicklime was effectively calcium-node-oriented, but there was a lack of sufficient integration between the fiber and the asphalt phase. Only when the three coupling agents were used synergistically in proportion did aggregate-fiber bridging, asphalt phase anchoring, and calcium node crosslinking occur simultaneously, resulting in the densest and most continuous interfacial network and optimal road performance. This is consistent with the results in Table 1 showing that Example 1 was superior to all comparative examples.

[0045] Example 2

[0046] This embodiment uses parameters and proportions within the lower limit of the range, based on Example 1. Activated coal gangue aggregate was obtained by calcining graded coal gangue at 550°C for 2.5 h, and its specific surface area was measured to be 6.5 m². 2 / g, surface pH is 8.4, the surface kaolinite partially dehydroxylates and transforms into a slightly alkaline amorphous phase. According to the formula, based on 100 parts by weight of activated coal gangue aggregate, there are 4 parts of asphalt binder, 0.2 parts of basalt fiber, 1 part of hydrated lime, and 0.3 parts of silane coupling component, including 0.15 parts of double-anchored bridging silane coupling agent, 0.08 parts of asphalt-anchored silane coupling agent, and 0.07 parts of calcium chelate bridging silane coupling agent.

[0047] The preparation process is the same as in Example 1: First, the silane coupling components are prepared into an ethanol hydrolysate with a pH of 4.5, sprayed onto activated coal gangue aggregate, and 0.3 parts of slaked lime are added for alkaline activation. The mixture is then stirred at 60°C for 30 min for surface coupling pre-coating and pore sealing. Next, basalt fibers are modified by 3% sodium hydroxide alkaline etching and silane impregnation. Subsequently, the coupled-modified activated coal gangue aggregate, modified basalt fibers, the remaining 0.7 parts of slaked lime, and 4 parts of mineral powder are dry-mixed at 160°C for 90 s. Finally, 4 parts of SBS modified bitumen heated to 165°C are sprayed in and hot-mixed at 165°C for 120 s to allow the interfacial coupling network to condense and solidify. The optimal asphalt-aggregate ratio for this example was determined to be 4.8% using Marshall design. This embodiment uses the lower limit parameters, with a lower activation temperature and a smaller amount of coupling components, yet it can still establish a continuous interface network between the aggregate and the fiber. However, its interface bonding density is slightly lower than that of Example 1, and the corresponding water stability and high-temperature stability indicators are slightly reduced.

[0048] The mixture obtained in this embodiment was characterized by X-ray diffraction, which showed that a small amount of kaolinite characteristic peaks remained in the coal gangue after activation at 550°C. The amorphous phase content was lower than that in Example 1, corresponding to a smaller number of condensable silanol groups on its surface. Therefore, the interfacial bonding density and water stability index were slightly lower than those in Example 1. However, compared with the comparative example using unactivated coal gangue, the water stability of this embodiment was still significantly improved due to surface activation and coupling agent bridging, confirming that the homologous co-coupling mechanism of the present invention is still effective even at the lower limit of the parameters.

[0049] Example 3

[0050] This embodiment uses parameters and proportions at the upper limit of the range, based on Embodiment 1. Activated coal gangue aggregate was obtained by calcining graded coal gangue at 850°C for 1.5 h, and its specific surface area was measured to be 9.6 m². 2 / g, surface pH 9.5, kaolinite fully dehydroxylated and transformed into amorphous metakaolinite phase without mullite formation. According to the formula, based on 100 parts by weight of activated coal gangue aggregate, there are 7 parts of asphalt binder, 0.5 parts of basalt fiber, 3 parts of hydrated lime, and 1.5 parts of silane coupling component, including 0.7 parts of double-anchored bridging silane coupling agent, 0.4 parts of asphalt-anchored silane coupling agent, and 0.4 parts of calcium chelate bridging silane coupling agent.

[0051] The preparation process was the same as in Example 1: the silane coupling component was prepared into an ethanol hydrolysate at pH 4.5 and sprayed onto activated coal gangue aggregate. 0.8 parts of slaked lime were added for alkaline activation, and the mixture was stirred at 60°C for 30 min for surface coupling pre-coating and pore sealing. Basalt fibers were modified by alkali etching and silane impregnation. The coupled-modified activated coal gangue aggregate, modified basalt fibers, 2.2 parts of the remaining slaked lime, and 6 parts of mineral powder were dry-mixed at 160°C for 90 s. Finally, 7 parts of SBS modified bitumen heated to 165°C were sprayed in and hot-mixed at 165°C for 120 s to allow the interfacial coupling network to condense and solidify. The optimal oil-aggregate ratio for this example was determined to be 5.2% using Marshall design. This example used the upper limit of the parameter range, achieving sufficient activation, a higher amount of coupling component, and the formation of a dense, continuous interfacial network between the aggregate and fibers, resulting in optimal water stability and high-temperature stability, thus verifying the effectiveness of the upper limit of the parameter range.

[0052] The mixture obtained in this embodiment was characterized by X-ray diffraction. The X-ray diffraction results showed that the characteristic peaks of kaolinite in the coal gangue completely disappeared after activation at 850°C, and no sharp mullite diffraction peaks appeared. The amorphous meta-kaolinite phase content was the highest, corresponding to the largest number of condensable silanol groups on its surface and the densest interfacial bonding. Therefore, its water stability and high-temperature stability were the best among the three embodiments. It should be noted that when the calcination temperature is further increased to above 850°C, mullite will be generated as shown in Comparative Example 5, leading to a decrease in the amorphous phase and surface activity. Therefore, the upper limit of the activation temperature in this invention is controlled at 850°C.

[0053] Comparative Example 1

[0054] This comparative example uses uncalcined and unactivated raw coal gangue aggregate, replacing the silane coupling component of this invention with an equal amount of conventional commercial monofunctional silane coupling agent (3-aminopropyltriethoxysilane). The remaining raw materials, proportions, and processes are the same as in Example 1. Since the coal gangue aggregate is unactivated, its surface remains acidic and inert, and contains adsorbed water, commercial monosilanes are difficult to effectively condense on its surface. Furthermore, monofunctional silanes can only modify aggregates or fibers individually and cannot form a continuous bridge between aggregates and fibers. The aggregates, fibers, and bitumen remain physically blended. This comparative example is used to verify the necessity of the innovative core of activation and homologous co-coupling continuous network.

[0055] Comparative Example 2

[0056] This comparative example uses conventional high-quality aggregate to replace coal gangue aggregate. Conventional limestone crushed stone aggregate replaces activated coal gangue aggregate, combined with basalt fiber and conventional commercial monosilane; the remaining proportions and processes are the same as in Example 1. This comparative example corresponds to the conventional technical solution of existing fiber-reinforced asphalt mixtures. Although limestone is an alkaline aggregate with good adhesion to asphalt, it does not utilize solid waste, and a continuous covalent network is not established between the aggregate and the fiber. It is used to compare and evaluate the performance level of this invention after replacing high-quality aggregate with activated coal gangue.

[0057] Comparative Example 3

[0058] This comparative example uses the same activated coal gangue aggregate as Example 1, but replaces the three coupling agents of this invention—dual-anchor bridging, bituminous anchoring, and calcium chelate bridging—with an equal amount of conventional commercial monofunctional silane coupling agents. The remaining proportions and processes are the same as in Example 1. Although the activated aggregate surface in this comparative example is active, the commercial monofunctional silanes cannot form a direct bridge between the aggregate and fibers, nor do they provide bituminous anchoring or calcium node functionality. This serves to verify the independent contribution of the molecular design of the three novel coupling agents of this invention relative to the innovation of the activated underlying layer.

[0059] Comparative Example 4

[0060] This comparative example uses uncalcined and unactivated raw coal gangue aggregate, combined with the three coupling agents of this invention: dual-anchor bridging, bituminous anchoring, and calcium chelate bridging. The remaining proportions and processes are the same as in Example 1. Because the surface of raw coal gangue is acidic and inert, with limited exposed silanol active sites and adsorbed water, the trialkoxysilane groups of the coupling agent of this invention are difficult to fully condense and anchor, making it difficult to establish a continuous interfacial network. This example serves as a prerequisite for verifying the alkaline active surface provided by calcination and activation to function as a molecularly designed coupling agent.

[0061] Comparative Example 5

[0062] This comparative example uses a calcination temperature exceeding the upper limit of the range of this invention. Coal gangue was calcined at 950°C for 2 hours, with the remaining proportions and process identical to Example 1. Due to the excessively high calcination temperature, mullite crystalline phases were generated in the activated coal gangue, resulting in a decrease in the content of amorphous silicon-aluminum phases, a reduction in surface active sites, and a decrease in the condensation anchoring density of the coupling agent. This was used to verify the technical significance of the 550~850°C activation temperature range of this invention.

[0063] Comparative Example 6

[0064] This comparative example lacks the slaked lime component. Based on Example 1, slaked lime is omitted, while the remaining proportions and process are the same. Due to the absence of slaked lime, the anti-stripping effect and the alkaline-activated silanol condensation effect are lost. Furthermore, the calcium chelating bridging silane coupling agent lacks a calcium ion source and cannot form calcium bridging nodes. This serves to verify the necessity of the triple function of slaked lime in this invention: anti-stripping, alkaline activation, and calcium node formation.

[0065] The asphalt mixtures obtained in each embodiment and comparative example were tested for road performance using the following methods. Freeze-thaw splitting strength ratio (TSR) was determined according to the freeze-thaw splitting test (T0729) in the current "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20). The ratio of the splitting tensile strength after freeze-thaw cycles to the unfrozen splitting tensile strength characterizes the resistance to water damage. The specification requires that the modified asphalt mixture have a TSR of not less than 80%. Residual stability after immersion was determined according to the Marshall test (T0709). The ratio of the Marshall stability after immersion for 48 hours to the standard Marshall stability characterizes the stability. The specification requires that the residual stability be not less than 85%. High-temperature rutting resistance was determined according to the dynamic stability of the rutting test (T0719), with units of cycles / mm. For heavy traffic, a value of not less than 3000 cycles / mm is typically required. Low-temperature crack resistance was determined according to the beam bending test (T0715), with the failure strain measured at -10°C, and the unit being microstrain. Marshall stability was determined according to the Marshall test of standard T0709, with units of kN. The optimal asphalt-aggregate ratio was determined by the Marshall volumetric design method, expressed as the percentage of asphalt mass to aggregate mass in the mixture. The adhesion between aggregate and asphalt was evaluated according to the boiling water method of T0616, characterized by grades 1 to 5, with grade 5 being the optimal grade. Three parallel specimens were taken for each test group, and the average value was taken.

[0066] The main instruments and operating points used in the above tests are as follows. In the freeze-thaw splitting test, the standard specimen was first vacuum-saturated with water for 15 min and then immersed in water for 0.5 h, followed by freezing at -18°C for 16 h, and then thawing in a 60°C water bath for 24 h. After completing one freeze-thaw cycle, it was loaded at 50 mm / min on a universal testing machine until failure, and the splitting tensile strength was recorded. The rutting test used a rutting testing machine, which was used to repeatedly drive the specimen at 60°C with a wheel pressure of 0.7 MPa, measuring the deformation between 45 min and 60 min and calculating the dynamic stability. The low-temperature beam bending test was performed at a constant temperature of -10°C with a mid-span loading of 50 mm / min until failure, and the failure strain was calculated from the mid-span deflection at failure. The adhesion boiling method test involved boiling the asphalt-coated aggregate in boiling water for 3 min, and the adhesion grade was assessed based on the area of ​​asphalt film peeling off. All specimens were molded and cured according to current specifications. Three parallel specimens were taken from each group, and the results were taken as the arithmetic mean, with the coefficient of variation controlled within the allowable range.

[0067] Table 1 shows the road performance test results of each embodiment and comparative example, with corresponding performance comparisons. Figure 3 .

[0068] Table 1. Road performance test results of each embodiment and comparative example

[0069] sample TSR / % Residual stability / % Dynamic stability (cycles / mm) Low-temperature failure strain / με Marshall stability / kN Optimal oilstone ratio / % Adhesion / Grade Example 1 95.2 96.8 7200 4150 14.2 5.0 5 Example 2 91.5 94.2 6100 3850 13.1 4.8 5 Example 3 93.8 95.5 6800 4050 13.8 5.2 5 Comparative Example 1 79.5 82.3 4200 3050 9.8 5.9 3 Comparative Example 2 87.5 89.2 5100 3250 11.5 4.9 4 Comparative Example 3 86.8 88.5 5400 3400 11.8 5.3 4 Comparative Example 4 83.2 85.1 4800 3200 10.9 5.7 4 Comparative Example 5 84.5 86.2 5000 3300 11.2 5.4 4 Comparative Example 6 85.5 87.0 5600 3450 12.0 5.2 4

[0070] As shown in Table 1, the road performance of the embodiments of the present invention is significantly better than that of the comparative examples, and its water stability even exceeds that of Comparative Example 2, which uses conventional limestone crushed stone, verifying that replacing high-quality aggregates with activated coal gangue solid waste does not reduce performance but rather improves it. More importantly, the comparison relationship between the comparative examples quantitatively reveals the nonlinear synergistic effect between the innovative activation base layer and the innovative coupling agent molecular design of the present invention. Taking the freeze-thaw splitting strength ratio (TSR) as an example: Comparative Example 1 (unactivated aggregate with commercial monosilane) has a TSR of 79.5%, which serves as the baseline; Comparative Example 3 (activated aggregate with commercial monosilane) has a TSR of 86.8%, meaning that the contribution of activation alone is 7.3 percentage points; Comparative Example 4 (unactivated aggregate with the coupling agent of this invention) has a TSR of 83.2%, meaning that the contribution of the coupling agent of this invention alone on the unactivated surface is only 3.7 percentage points; If the contributions of the two are simply added together, the predicted value should be 79.5% + 7.3 + 3.7 = 90.5%, while the measured value of Example 1 (activated aggregate with the coupling agent of this invention) reaches 95.2%, exceeding the predicted value by 4.7 percentage points. This excess portion represents the nonlinear synergy between activation and molecular design: the dual-anchor bridging coupling agent of this invention must fully condense and form a continuous bridging network on the alkaline silica-alumina active surface provided by activation, while the activated surface must also rely on the dual-anchor bridging coupling agent to integrate the aggregate and fiber into a continuously stressed whole. Both are prerequisites and indispensable, thus generating a synergistic effect exceeding the sum of their individual contributions. Comparative Examples 5 and 6 further demonstrate that calcination temperatures exceeding the upper limit of 850°C, resulting in mullite formation, or the absence of hydrated lime, both significantly reduce performance, verifying the technical significance of the triple effect of the activation temperature range and hydrated lime.

[0071] The aforementioned nonlinear synergy is reflected not only in the freeze-thaw splitting strength ratio but also in high-temperature and low-temperature performance and the oilstone ratio. Regarding dynamic stability, Comparative Example 3 (activated aggregate with commercial monosilane) achieved 5400 cycles / mm, Comparative Example 4 (unactivated aggregate with the coupling agent of this invention) achieved 4800 cycles / mm, while Example 1 reached 7200 cycles / mm, significantly higher than the predicted value obtained by simply adding the increments of Comparative Example 1's 4200 cycles / mm. This is because the fibers can only fully exert their reinforcing bridging effect and avoid pull-out under load after being chemically anchored on the activated surface by the coupling agent, thus greatly improving rutting resistance. Regarding low-temperature failure strain, Example 1's 4150 με is also higher than Comparative Example 3's 3400 με and Comparative Example 4's 3200 με, indicating that the continuous interface network can effectively transfer and disperse stress and inhibit crack initiation at low temperatures. Regarding the optimal asphalt-aggregate ratio, Comparative Example 1 had an asphalt-aggregate ratio as high as 5.9% due to the unactivated and porous nature of the coal gangue, while Example 1 had an asphalt-aggregate ratio as low as 5.0% due to the pre-coating of coupling components to seal pores and reduce free asphalt absorption. This resulted in a reduction in asphalt usage while achieving the same or even better performance, thus gaining multiple benefits such as economy, carbon reduction, and rutting resistance. This is contrary to the conventional understanding that using porous waste aggregates usually increases the asphalt-aggregate ratio.

[0072] From an engineering application perspective, the freeze-thaw splitting strength ratio of each embodiment of this invention reaches over 90%, the residual stability after immersion in water reaches over 94%, the dynamic stability reaches over 6000 cycles / mm, and the low-temperature failure strain reaches over 3800 με. These performances comprehensively surpass the current specifications for modified asphalt mixtures, which require water stability of no less than 80%, residual stability of no less than 85%, and dynamic stability under heavy traffic of no less than 3000 cycles / mm. Furthermore, compared to Comparative Example 2, which uses conventional limestone aggregate, this invention shows significant improvements in water stability, high-temperature stability, and low-temperature crack resistance. This indicates that this invention not only solves the problems of water damage and high asphalt-aggregate ratio when using coal gangue as asphalt aggregate, but also enables asphalt mixtures with solid waste as the main component to reach or even exceed the road performance levels of high-quality aggregate mixtures. It possesses significant engineering value and environmental benefits such as solid waste resource utilization and carbon reduction, making it suitable for paving road surfaces, bridge decks, and mining roads.

[0073] The comprehensive synergy of this invention stems from the combined effects of activation, homologous co-coupling, and the dual effects of quicklime. Coal gangue is calcined at a controlled temperature of 550~850°C to remove hydroxyl groups, transforming the surface kaolinite into a slightly alkaline amorphous slightly alkaline phase. The originally acidic, inert surface containing adsorbed water is cleaned, opened, and transformed into a slightly alkaline active surface exposing silicon-oxygen and aluminum-oxygen active sites. This activation not only provides a large number of condensable surface silanol groups for subsequent silane coupling, but also transforms the originally unfavorable porous structure into a favorable space for mechanical interlocking and interfacial anchoring. Since activated coal gangue aggregate and basalt fiber are both siliceous and aluminous with homologous surface chemistry, this invention allows for the simultaneous bonding of the two using the same silane coupling system: the trialkoxysilane groups at both ends of the dual-anchor bridging silane coupling agent condense with the aggregate surface and fiber surface respectively, forming a direct covalent bridge at the interface between the aggregate and fiber; the coupling layers grafted onto each surface are compatible with and anchored to the asphalt through their organic segments, thereby upgrading the aggregate, fiber, and asphalt from a traditional three-phase physical blend to a continuously stressed three-phase chemical symbiotic network. Figure 2 As shown, this continuous network allows interfacial stress to be continuously transferred between aggregates, fibers, and asphalt. Fibers are transformed from physically dispersed to chemically anchored, making them less prone to pull-out. Water molecules are less likely to penetrate and disrupt the covalently bonded interfaces, thus simultaneously improving water stability, high-temperature rutting resistance, and low-temperature crack resistance. Quicklime plays a triple role in this system: it acts as an anti-stripping agent, bridging acidic asphalt and aggregates with calcium ions; it acts as an alkaline activator, raising the system pH and catalyzing silanol condensation; and it serves as a source of calcium ions, chelating and bridging the β-dicarbonyl groups of the silane coupling agent to form chemical bonding nodes in the network. These three roles reinforce each other, overcoming the shortcomings of existing technologies where quicklime only undergoes physical adsorption.

[0074] Furthermore, the homologous co-coupling mechanism revealed in this invention breaks through the inherent design of traditional fiber-reinforced asphalt mixtures, which treat aggregates as inert skeletons and fibers as isolated reinforcing phases, and only physically blend the two with asphalt. In this invention, aggregates and fibers are no longer two unrelated phases, but are integrated into a continuously stressed interface through the same silane coupling system by leveraging their homologous surface chemistry of silicon and aluminum. Coal gangue, a solid waste that is originally weak, porous, and poorly adhered, has its surface defects transformed into advantages of interface coupling and mechanical interlocking after calcination and activation, thus achieving the counterintuitive effect of replacing high-quality aggregates with solid waste while improving performance. This effect is not a simple superposition of the properties of each component, but a system-level synergy produced by the coupling of activation, homologous co-coupling, and quicklime, which is difficult to obtain obviously by modifying aggregates or fibers alone in existing technologies.

[0075] From a molecular perspective, the formation of the interfacial symbiotic network of this invention includes three stages: silane hydrolysis, surface condensation, and interfacial bonding. In the surface coupling pre-coating stage, the triethoxysilyl group of the silane coupling component hydrolyzes in a weakly acidic hydrolysis solution to generate silanol groups. The reaction involves the triethoxysilyl group reacting with water to generate silanetriol and release ethanol. Subsequently, on the surface of activated coal gangue aggregate and basalt fiber, the silanol groups undergo dehydration condensation with surface silanol and aluminol groups, forming Si—O—Si and Si—O—Al covalent bonds, respectively, firmly grafting the coupling agent onto the silicoaluminous surface. Because the activated coal gangue surface is rich in silicon-oxygen and aluminum-oxygen active sites exposed due to dehydroxylation reconstruction, and the alkaline environment provided by slaked lime promotes silanol condensation, the condensation reaction proceeds efficiently. This is precisely why the unactivated aggregate in Comparative Example 4 struggled to establish a continuous network.

[0076] For the dual-anchored bridging silane coupling agent 3-(4,4-diethoxy-9-oxadienyl-8-aza-3-oxa-4-silanon-9-yl)-N-(4,4-diethoxy-3-oxa-4-silanoheptane-7-yl)-5-(dodecyloxy)benzamide, each end of its molecule has a triethoxysilyl group. After hydrolysis and condensation, the two ends are anchored to the surface of aggregate and fiber, respectively, forming a covalent molecular bridge at the interface between the two, allowing the aggregate and fiber to bond directly. The benzene ring and dodecyloxy long chain in the center of its molecule are compatible with the aromatic and saturated components in asphalt, and the molecular bridge is incorporated into the asphalt mastic through π-π interactions and van der Waals forces, thus ensuring good bonding between the bridging zone and the asphalt. For the asphaltene-anchored silane coupling agent N-(4,4-diethoxy-3-oxa-4-silazept-7-yl)-5-octylthiophene-2-carboxamide, its triethoxysilyl group is anchored to the surface of aggregates or fibers, while its thiophene ring, due to its similarity to the thiophene sulfur and fused aromatic ring structure abundant in asphaltene, is embedded into the asphaltene aggregate through π-π stacking and coordination with sulfur atoms, actively anchoring the asphalt phase into the inorganic network, thus compensating for the deficiency of the bridging zone and the asphalt interface when relying solely on dual-anchor bridging coupling agents. For the calcium chelating bridging silane coupling agent 2-(4,4-diethoxy-9-oxylidene-8-aza-3-oxa-4-silanenon-9-yl)-N-(4,4-diethoxy-3-oxa-4-silaneheptane-7-yl)-3-oxylidenebutyramide, the acetyl group in the center of its molecule forms a β-dicarbonyl structure with the adjacent amide carbonyl group. Under alkaline conditions, it provides two oxygen coordination sites in an enol form, chelating the calcium ions released by slaked lime in a bidentate manner. This transforms the slaked lime, which was originally only physically adsorbed on the aggregate surface, into bridging nodes centered on calcium ions and incorporated into the network through chelation and siloxane condensation. This not only blocks the residual alkaline active sites and micropores on the activated aggregate surface, thus improving water resistance, but also introduces additional calcium bridging crosslinking points into the network, thereby strengthening the integrity of the aggregate-fiber-asphalt continuous network. The three coupling agents mentioned above work synergistically and complement each other in the coupling components, respectively undertaking aggregate-fiber bridging, asphalt phase anchoring and calcium node crosslinking, and jointly constructing a continuously stressed interfacial symbiotic network. This is the chemical essence of the significant improvement in various road performance characteristics and the nonlinear synergistic effect of the present invention.

[0077] From an energy and durability perspective, the advantage of the interface network in this invention lies in replacing the physical adsorption between aggregates and asphalt, and between fibers and asphalt in traditional asphalt mixtures with covalent bonds. Physical adsorption interfaces are prone to delamination under competitive adsorption by water molecules, which is the microscopic root cause of water damage. In contrast, the interfaces of this invention, connected by Si-O-Si, Si-O-Al covalent bonds and calcium chelate nodes, have bond energies far exceeding those of van der Waals forces and hydrogen bonds, making them difficult for water molecules to break. Therefore, the strength retention rate after freeze-thaw cycles is high. Simultaneously, the continuous network integrates the aggregate skeleton, fiber reinforcement phase, and asphalt cementitious phase into a unified stress-bearing system. External loads are continuously transferred between the three phases through the coupling layer, avoiding stress concentration and debonding at the physical interfaces. The fiber ends are anchored to the aggregate through the coupling layer, and under tension, the load is borne by chemical bonds rather than friction, thus fully and persistently exerting its reinforcing and bridging effect. These covalent, continuous, and integrated characteristics constitute the fundamental reason for the simultaneous improvement in water stability, high-temperature rutting resistance, and low-temperature crack resistance in this invention.

[0078] The chemical basis of asphaltene anchoring needs further explanation. Asphalt is a complex colloidal system composed of saturated components, aromatic components, resins, and asphaltene. Among them, asphaltene is the component with the largest relative molecular mass and the strongest polarity. It is rich in heteroatom functional groups such as fused aromatic rings, thiophene sulfur, pyridine nitrogen, and carboxyl groups, and exists in the form of aggregates in asphalt. It is a key component that determines the high-temperature performance and aging behavior of asphalt. The asphaltene anchoring silane coupling agent of this invention introduces a thiophene ring at the end of the molecule. This is based on the high structural similarity between the thiophene ring and the naturally occurring thiophene sulfur and fused aromatic rings in asphaltene. The thiophene ring can be inserted into the fused aromatic lamellae of asphaltene through π-π stacking. Its sulfur atoms can coordinate and disperse with heteroatom sites in the asphaltene aggregates, thereby anchoring the asphaltene aggregates through chemical affinity rather than simple physical coating. The asphalt phase is firmly bound to the inorganic network on the surface of the activated aggregates through the triethoxysilyl group at the other end of the molecule. Therefore, the asphalt phase is no longer a continuous medium that is physically adhered to the aggregate surface, but an organic phase that is actively anchored into the aggregate-fiber inorganic network through asphalt aggregates. This is the molecular-level reason why the present invention can maintain interface integrity and inhibit asphalt film peeling under repeated loading and water coupling.

[0079] In terms of reaction kinetics, the hydrolysis and condensation of the silane coupling components are jointly regulated by the system's pH, temperature, and water volume. During the surface coupling pre-coating stage, adjusting the pH of the hydrolysate to a weakly acidic range of 4-5 allows for the moderate hydrolysis of triethoxysilyl groups into silanols without excessive self-condensation, ensuring that the coupling agent penetrates the aggregate pores in monomer or oligomer form and is evenly distributed on the surface. The subsequent addition of slaked lime provides an alkaline environment that accelerates the condensation of silanols with surface hydroxyl groups, resulting in a stable grafted coupling layer on the aggregate surface. During the hot-mix stage, the high temperature of 160-170°C further drives the dehydration condensation of residual silanols and the solidification of interfacial bonds, ultimately forming the covalent network between the aggregate, fiber, and asphalt. It is this phased regulation—first controlling hydrolysis with weak acid, then promoting condensation with alkaline solution, and finally curing at high temperature—that enables the coupling components of this invention to not only fully penetrate and seal pores, but also form a dense and continuous covalent bond layer at the interface. This is the process basis for this invention, which distinguishes it from the conventional practice of simply adding a single silane into asphalt or aggregate and achieves significant synergistic effects.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A basalt fiber reinforced coal gangue asphalt mixture, characterized in that, The composition, by weight, comprises 100 parts activated coal gangue aggregate, 4-7 parts asphalt binder, 0.2-0.5 parts basalt fiber, 1-3 parts hydrated lime, and 0.3-1.5 parts silane coupling component; the asphalt binder is base asphalt or SBS modified asphalt; the activated coal gangue aggregate is coal gangue particles that have undergone dehydroxylation through controlled calcination at 550-850°C; the silane coupling component consists of a dual-anchored bridging silane coupling agent, an asphalt-based anchored silane coupling agent, and a calcium-chelated bridging silane coupling agent, with a weight ratio of (2-4):(1-2):(1-2); the dual-anchored bridging silane coupling agent is 3-(4,4-diethoxy) -9-oxoylide-8-aza-3-oxa-4-silane-non-9-yl)-N-(4,4-diethoxy-3-oxa-4-silane-hept-7-yl)-5-(dodecyloxy)benzamide; the asphaltene-anchored silane coupling agent is N-(4,4-diethoxy-3-oxa-4-silane-hept-7-yl)-5-octylthiophene-2-carboxamide; the calcium chelating bridging silane coupling agent is 2-(4,4-diethoxy-9-oxoylide-8-aza-3-oxa-4-silane-non-9-yl)-N-(4,4-diethoxy-3-oxa-4-silane-hept-7-yl)-3-oxoylide butyramide.

2. The basalt fiber reinforced coal gangue pitch mixture according to claim 1, characterized in that, The silane coupling component is pre-coated into the open pores of the activated coal gangue aggregate and seals the pore openings.

3. The method for preparing basalt fiber reinforced coal gangue asphalt mixture as described in claim 1 or 2, characterized in that, The process includes the following steps: (1) crushing and classifying coal gangue and calcining it at a controlled temperature of 550~850°C to remove residual carbon and dehydroxylate the kaolinite on its surface to transform it into a slightly alkaline amorphous silicon-aluminum phase, thereby obtaining activated coal gangue aggregate; (2) preparing the silane coupling component into a hydrolysate and performing wet surface coupling pre-coating and pore sealing on the activated coal gangue aggregate, during which some quicklime is added to activate the silanol condensation; (3) performing silane coupling or alkaline etching surface modification on basalt fiber to expose its surface silanol; (4) dry mixing the activated coal gangue aggregate obtained in step (2), the basalt fiber obtained in step (3), the remaining quicklime, and mineral powder; (5) spraying in heated asphalt binder for hot mixing, so that the silane coupling component further condenses and solidifies in a hot state, and then spreading and compacting to obtain the basalt fiber reinforced coal gangue asphalt mixture.

4. The application of the basalt fiber reinforced coal gangue asphalt mixture as described in claim 1 or 2 in road surface layers, bridge deck paving, or mining road paving.

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