Freeze-thaw resistant concrete for cold region highway and preparation method thereof

Abstract

The present invention discloses a freeze-thaw resistant concrete for cold-region highways and a preparation method thereof, and relates to the field of concrete technology. The preparation method comprises the following steps: dry-mixing silicate cement, kaolin, and silicon carbide whiskers, then adding coarse aggregate and fine aggregate and continuing to stir and mix uniformly to obtain a premix, then adding a water reducer and water to the premix, continuing to stir and mix uniformly to obtain freeze-thaw resistant concrete. The present invention adds an appropriate amount of silicon carbide whiskers to the mixed soil, which has high strength, high elastic modulus, and excellent chemical stability. It can significantly improve the concrete's ability to resist freeze-thaw cycles by bridging microcracks, hindering crack propagation paths, and improving pore structure.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, in particular to freeze-thaw resistant concrete for cold region roads and a preparation method thereof. Background Art

[0002] Portland cement is a hydraulic binder primarily composed of calcium silicate. It consists of Portland cement clinker, an appropriate amount of gypsum, and specified admixtures. Due to its high early strength, rapid setting and hardening, and excellent bonding properties, it is widely used as a concrete binder in highway construction. However, in cold-region highway construction, concrete structures are subject to the harsh environmental conditions of long-term freeze-thaw cycles. This involves the water in the concrete pores freezing and expanding at low temperatures, generating stress that can repeatedly damage the concrete structure. Portland cement-based concrete inherently suffers from significant freeze-thaw resistance deficiencies. The cement hydration process forms numerous interconnected pores, which readily become saturated with water. During freeze-thaw cycles, the stresses generated by the freezing and expansion of water within the pores cause microcracks within the concrete to expand, gradually degrading the cement paste's microstructure. Especially when the ambient temperature fluctuates frequently around 0°C, the frequency of freeze-thaw cycles increases, and microcracks can rapidly interconnect, forming macrocracks that compromise the concrete's integrity.

[0003] At present, although traditional measures to improve the freeze-thaw resistance of concrete (such as adding air-entraining agents, increasing cement content, optimizing aggregate grading, etc.) can delay freeze-thaw damage to a certain extent, they have limitations such as excessive air entrainment leading to a significant decrease in strength, increased cement content causing shrinkage cracking, and aggregate grading optimization being restricted by construction conditions. It is difficult to fundamentally solve the problem of insufficient freeze-thaw resistance of concrete for cold-region highways. Summary of the Invention

[0004] The present invention aims to provide a solution to the technical problem of insufficient freeze-thaw resistance of concrete for cold-region highways, as identified in the aforementioned background art. By adding an appropriate amount of silicon carbide whiskers to the soil mix, the present invention significantly improves concrete's freeze-thaw resistance by bridging microcracks, hindering crack propagation paths, and improving pore structure.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A freeze-thaw resistant concrete for cold region roads, comprising the following components in parts by weight:

[0007] 80-100 parts of coarse aggregate, 60-70 parts of fine aggregate, 35-45 parts of Portland cement, 30-40 parts of kaolin, 10-15 parts of silicon carbide whiskers, 0.3-0.8 parts of water reducer, and 20-30 parts of water.

[0008] In this technical solution, coarse aggregate forms the mechanical skeleton, while fine aggregate fills the voids and optimizes gradation. Portland cement provides strength as the cementitious bulk, while calcined kaolin refines pores through the pozzolanic effect. Silicon carbide whiskers form a three-dimensional network within the concrete, exhibiting high strength, high elastic modulus, and excellent chemical stability. This network significantly enhances the concrete's freeze-thaw resistance by bridging microcracks, hindering crack propagation paths, and improving pore structure. Polycarboxylate superplasticizers reduce the water-cement ratio to improve density. This system, through the synergistic effects of dense aggregate packing, optimized filler porosity, and fiber toughening, imparts excellent freeze-thaw resistance to concrete.

[0009] Preferably, the coarse aggregate is selected from one or more of granite crushed stone, basalt crushed stone and limestone crushed stone.

[0010] Preferably, the coarse aggregate has a particle size of 10-20 mm and a mud content of ≤0.5%.

[0011] Preferably, the fine aggregate is selected from one or more of natural river sand and machine-made sand.

[0012] Preferably, the fine aggregate has a fineness modulus of 2.3-3.0, a mud content ≤1.0%, and a chloride ion content ≤0.02%.

[0013] Preferably, the silicon carbide whiskers are subjected to a modification process comprising the following steps:

[0014] S1, adding the halloysite nanotubes to a hydrochloric acid solution, performing acid activation treatment under heating conditions, and performing centrifugal separation, washing, and drying to obtain activated halloysite nanotubes;

[0015] S2, polytetrahydrofuran diol, isophorone diisocyanate and catalyst are heated to react under nitrogen protection, and then dimethylol propionic acid continues to react to obtain a polyurethane prepolymer;

[0016] S3, mixing the activated halloysite nanotubes and the polyurethane prepolymer, then adding acetone solvent to uniformly disperse them by ultrasonication, and then adding deionized water containing triethylamine to perform shear emulsification to obtain a composite emulsion;

[0017] S4. Immersing the silicon carbide whiskers in a composite emulsion to coat the surface of the plasma-treated silicon carbide whiskers with an emulsion coating, then placing them in an oven for drying and curing, and then irradiating them with ultraviolet light to obtain modified silicon carbide whiskers.

[0018] In the technical solution of the present invention, to further improve the freeze-thaw resistance of concrete, the present invention modifies silicon carbide whiskers. First, the halloysite nanotubes are acid-activated and etched with a hydrochloric acid solution to expose more active groups on their surface, while also improving the dispersibility of the nanotubes. Then, polytetramethylene glycol and isophorone diisocyanate are used to undergo a condensation reaction to synthesize a reactive polyurethane prepolymer. The activated halloysite nanotubes are then composited with the polyurethane prepolymer. The hydroxyl groups on the halloysite surface react with the -NCO groups on the polyurethane prepolymer to form a covalent bond, thereby increasing the bonding strength between the two. Finally, the silicon carbide whiskers are immersed in the composite emulsion, thermally cured, and irradiated with ultraviolet light, and then coated with a nano-enhanced polymer multifunctional coating on the surface of the silicon carbide whiskers. The inner cavity of the halloysite selectively adsorbs free water, reducing the freezable water content of the concrete. The polyurethane forms a hydrophobic barrier, increasing the coating contact angle, reducing water penetration into the concrete, and lowering the chloride ion permeability coefficient. Furthermore, the polyurethane in the coating acts as an elastic buffer, absorbing frost heave strain during freeze-thaw cycles, thereby protecting the concrete from damage. The nano-enhanced polymer coating on the surface of the silicon carbide whiskers imparts stress-transfer capabilities and water-blocking and water-absorbing properties, significantly enhancing the long-term durability of concrete in harsh freeze-thaw environments.

[0019] Preferably, in step S2, the mass ratio of polytetrahydrofuran diol to isophorone diisocyanate is 5:1-2.

[0020] Preferably, in step S3, the mass ratio of the polyurethane prepolymer to the activated halloysite nanotubes is 10:2-3.

[0021] Preferably, in step S4, the silicon carbide whiskers are pretreated, comprising the following steps:

[0022] performing surface plasma treatment on silicon carbide whiskers to obtain plasma-treated silicon carbide whiskers;

[0023] The plasma-treated silicon carbide whiskers are grafted with acrylic acid vapor, vacuum annealed, ultrasonically dispersed and washed in anhydrous ethanol to obtain the product.

[0024] In the technical solution of the present invention, as mentioned above, the nano-enhanced polymer coating coated on the surface of silicon carbide whiskers realizes the improvement of silicon carbide whiskers to the freeze-thaw performance of concrete. However, the present invention team finds that modified silicon carbide whiskers are mixed in concrete, and in the external force stirring and mixing process, a strong friction effect is generated between the materials, and the nano-enhanced polymer coating coated on the surface of silicon carbide whiskers easily falls off from its surface, thereby reducing its improvement effect on the freeze-thaw resistance of concrete. The present invention is to further solve this problem, and silicon carbide whiskers are pre-treated, and acrylic acid is grafted on its surface to make its surface load-COOH, and-NCO in the polyurethane prepolymer in the COOH and nano-enhanced polymer coating is reacted to form a covalent bond, thereby silicon carbide whiskers and nano-enhanced polymer coating are bonded by chemical bonds, significantly improving the bonding strength of the two, avoiding subsequent coating to fall off from the silicon carbide whisker surface, maintaining the stability of the two combinations, and realizing the further improvement effect on the freeze-thaw resistance of concrete.

[0025] A method for preparing freeze-thaw resistant concrete for cold region roads comprises the following steps:

[0026] Dry-mixing silicate cement, kaolin, and silicon carbide whiskers, then adding coarse aggregate and fine aggregate and continuing to stir and mix uniformly to obtain a premix;

[0027] Add water reducing agent and water to the premix and continue to stir evenly to obtain freeze-thaw resistant concrete.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. Coarse and fine aggregates form a skeleton and optimize gradation, cement and kaolin form a dense matrix, silicon carbide whiskers bridge cracks and enhance toughness, and water-reducing agents reduce the water-cement ratio, synergistically improving freeze-thaw resistance. 2. Activated halloysite is compounded with a polyurethane prepolymer, coating the silicon carbide whiskers to form a coating. This coating enhances concrete's durability in harsh environments by adsorbing free water, providing hydrophobicity and permeability resistance, and providing elastic cushioning. 3. Pre-treated silicon carbide whiskers are grafted with acrylic acid, forming covalent bonds between the -COOH group and the -NCO group in the coating, preventing the coating from falling off during mixing and steadily improving the concrete's freeze-thaw resistance. DETAILED DESCRIPTION

[0030] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the implementation regulations described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0031] Example 1

[0032] A freeze-thaw resistant concrete for cold region roads, comprising the following components in parts by weight:

[0033] 95 parts of coarse aggregate (granite crushed stone, particle size 10-20mm, mud content ≤0.5%), 68 parts of fine aggregate (natural river sand, fineness modulus 2.5, mud content ≤1.0%, chloride ion content ≤0.02%), 43 parts of Portland cement (PO 42.5), 39 parts of kaolin, 14 parts of silicon carbide whiskers (particle size 5-10μm, length 300-500μm), 0.7 parts of polycarboxylate water reducer (solid content 30%), and 28 parts of water.

[0034] A method for preparing freeze-thaw resistant concrete for cold region roads comprises the following steps:

[0035] Add Portland cement, kaolin, and silicon carbide whiskers into a blender and dry mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue stirring for 8 minutes to mix thoroughly to obtain a premix;

[0036] Add water reducing agent and water to the premix, and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0037] Example 2

[0038] A freeze-thaw resistant concrete for cold region roads, comprising the following components in parts by weight:

[0039] 95 parts of coarse aggregate (granite crushed stone, particle size 10-20mm, mud content ≤0.5%), 68 parts of fine aggregate (natural river sand, fineness modulus 2.5, mud content ≤1.0%, chloride ion content ≤0.02%), 43 parts of Portland cement (PO 42.5), 39 parts of kaolin, 14 parts of modified silicon carbide whiskers, 0.7 parts of polycarboxylate water reducer (solid content 30%), and 28 parts of water.

[0040] The preparation method of modified silicon carbide whiskers comprises the following steps:

[0041] Step S1: 10 g of silicon carbide whiskers (5-10 μm in diameter, 300-500 μm in length) were spread on the plasma reactor tray, oxygen was introduced (flow rate 50 sccm), and the vacuum was evacuated to 10 -2 Pa, treated with 80W power for 3 minutes to activate the surface; then transferred to a vacuum reactor and reacted with 5mL of acrylic acid vapor at 70℃ and 1kPa for 2 hours to achieve grafting; nitrogen was introduced for cooling after the reaction, and vacuum annealing was performed at 100℃ for 1 hour to eliminate stress, and then ultrasonically dispersed with 200mL of anhydrous ethanol (300W, 15 minutes) and centrifuged (4000rpm, 10 minutes) 3 times, and finally vacuum dried at 60℃ for 12 hours to obtain pretreated whiskers.

[0042] Step S2: 20 g of halloysite nanotubes (diameter 10-30 nm, length 1-5 μm) were added to 200 mL of 3 mol / L hydrochloric acid solution and etched in an 80°C oil bath at 300 rpm with magnetic stirring for 4 hours. After the reaction, the nanotubes were centrifuged (5000 rpm) and repeatedly washed with deionized water until the filtrate had a pH of 7. The solid was vacuum dried at 80°C for 24 hours to obtain activated halloysite with an increased surface hydroxyl density.

[0043] Step S3: 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) was vacuum dried at 110° C. for 2 hours to remove water, then cooled to room temperature and placed in a three-necked flask. 18 g of isophorone diisocyanate (IPDI) and 0.1 g of dibutyltin dilaurate catalyst were added in sequence, nitrogen was introduced for protection, and the mixture was reacted at 80° C. for 2 hours. Subsequently, 5 g of dimethylolpropionic acid (DMPA) was added, and the reaction was continued at 70° C. for 3 hours to synthesize a terminal -NCO polyurethane prepolymer, which was then sealed for later use.

[0044] Step S4: 14 g of activated halloysite and 50 g of polyurethane prepolymer were mixed, 100 mL of acetone was added, and ultrasonic dispersion was performed (400 W, 30 minutes) to form a uniform suspension; 200 mL of deionized water containing 5 mL of triethylamine was slowly added dropwise, and 1.3 g of benzoin dimethyl ether was added as a photosensitizer. The mixture was sheared and emulsified at 10,000 rpm for 20 minutes, and the acetone was removed by vacuum distillation (40°C, 10 kPa) to obtain a composite emulsion;

[0045] Step S5: 10 g of pretreated silicon carbide whiskers were immersed in the composite emulsion and stirred for 2 hours. After being taken out, the coating was dried at 80°C for 12 hours to solidify the coating, and then irradiated with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for cross-linking to obtain modified silicon carbide whiskers.

[0046] A method for preparing freeze-thaw resistant concrete for cold region roads comprises the following steps:

[0047] Add Portland cement, kaolin, and modified silicon carbide whiskers into a blender and dry mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue stirring for 8 minutes to mix evenly to obtain a premix;

[0048] Add water reducing agent and water to the premix, and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0049] Example 3

[0050] A freeze-thaw resistant concrete for cold region roads, comprising the following components in parts by weight:

[0051] Coarse aggregate (basalt crushed stone, particle size 10-20mm, mud content ≤0.5%) 85 parts, fine aggregate (machine-made sand, fineness modulus 2.5, mud content ≤1.0%, chloride ion content ≤0.02%) 62 parts, Portland cement (PO 42.5) 38 parts, kaolin 32 parts, modified silicon carbide whisker 13 parts, polycarboxylate water reducer (solid content 30%) 0.4 parts, water 22 parts.

[0052] The preparation method of modified silicon carbide whiskers comprises the following steps:

[0053] Step S1: 10 g of silicon carbide whiskers (5-10 μm in diameter, 300-500 μm in length) were spread on the plasma reactor tray, oxygen was introduced (flow rate 50 sccm), and the vacuum was evacuated to 10 -2 Pa, treated with 80W power for 3 minutes to activate the surface; then transferred to a vacuum reactor and reacted with 5mL of acrylic acid vapor at 70℃ and 1kPa for 2 hours to achieve grafting; nitrogen was introduced for cooling after the reaction, and vacuum annealing was performed at 100℃ for 1 hour to eliminate stress, and then ultrasonically dispersed with 200mL of anhydrous ethanol (300W, 15 minutes) and centrifuged (4000rpm, 10 minutes) 3 times, and finally vacuum dried at 60℃ for 12 hours to obtain pretreated whiskers.

[0054] Step S2: 20 g of halloysite nanotubes (diameter 10-30 nm, length 1-5 μm) were added to 200 mL of 3 mol / L hydrochloric acid solution and etched in an 80°C oil bath at 300 rpm with magnetic stirring for 4 hours. After the reaction, the nanotubes were centrifuged (5000 rpm) and repeatedly washed with deionized water until the filtrate had a pH of 7. The solid was vacuum dried at 80°C for 24 hours to obtain activated halloysite with an increased surface hydroxyl density.

[0055] Step S3: 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) was vacuum dried at 110° C. for 2 hours to remove water, then cooled to room temperature and placed in a three-necked flask. 13 g of isophorone diisocyanate (IPDI) and 0.1 g of dibutyltin dilaurate catalyst were added in sequence, nitrogen was introduced for protection, and the mixture was reacted at 80° C. for 2 hours. Subsequently, 5 g of dimethylolpropionic acid (DMPA) was added, and the reaction was continued at 70° C. for 3 hours to synthesize a terminal -NCO polyurethane prepolymer, which was then sealed for later use.

[0056] Step S4: 12 g of activated halloysite and 50 g of polyurethane prepolymer were mixed, 100 mL of acetone was added, and ultrasonic dispersion was performed (400 W, 30 minutes) to form a uniform suspension; 200 mL of deionized water containing 5 mL of triethylamine was slowly added dropwise, and 1.3 g of benzoin dimethyl ether was added as a photosensitizer. The mixture was sheared and emulsified at 10,000 rpm for 20 minutes, and the acetone was removed by vacuum distillation (40°C, 10 kPa) to obtain a composite emulsion;

[0057] Step S5: 10 g of pretreated silicon carbide whiskers were immersed in the composite emulsion and stirred for 2 hours. After being taken out, the coating was dried at 80°C for 12 hours to solidify the coating, and then irradiated with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for cross-linking to obtain modified silicon carbide whiskers.

[0058] A method for preparing freeze-thaw resistant concrete for cold region roads comprises the following steps:

[0059] Add Portland cement, kaolin, and modified silicon carbide whiskers into a blender and dry mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue stirring for 8 minutes to mix evenly to obtain a premix;

[0060] Add water reducing agent and water to the premix, and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0061] Example 4

[0062] A freeze-thaw resistant concrete for cold region roads, comprising the following components in parts by weight:

[0063] 90 parts of coarse aggregate (limestone crushed stone, particle size 10-20mm, mud content ≤0.5%), 65 parts of fine aggregate (natural river sand, fineness modulus 2.5, mud content ≤1.0%, chloride ion content ≤0.02%), 40 parts of Portland cement (PO 42.5), 35 parts of kaolin, 13 parts of modified silicon carbide whiskers, 0.5 parts of polycarboxylate water reducer (solid content 30%), and 25 parts of water.

[0064] The preparation method of modified silicon carbide whiskers comprises the following steps:

[0065] Step S1: 10 g of silicon carbide whiskers (5-10 μm in diameter, 300-500 μm in length) were spread on the plasma reactor tray, oxygen was introduced (flow rate 50 sccm), and the vacuum was evacuated to 10 -2 Pa, treated with 80W power for 3 minutes to activate the surface; then transferred to a vacuum reactor and reacted with 5mL of acrylic acid vapor at 70℃ and 1kPa for 2 hours to achieve grafting; nitrogen was introduced for cooling after the reaction, and vacuum annealing was performed at 100℃ for 1 hour to eliminate stress, and then ultrasonically dispersed with 200mL of anhydrous ethanol (300W, 15 minutes) and centrifuged (4000rpm, 10 minutes) 3 times, and finally vacuum dried at 60℃ for 12 hours to obtain pretreated whiskers.

[0066] Step S2: 20 g of halloysite nanotubes (diameter 10-30 nm, length 1-5 μm) were added to 200 mL of 3 mol / L hydrochloric acid solution and etched in an 80°C oil bath at 300 rpm with magnetic stirring for 4 hours. After the reaction, the nanotubes were centrifuged (5000 rpm) and repeatedly washed with deionized water until the filtrate had a pH of 7. The solid was vacuum dried at 80°C for 24 hours to obtain activated halloysite with an increased surface hydroxyl density.

[0067] Step S3: 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) was vacuum dried at 110° C. for 2 hours to remove water, then cooled to room temperature and placed in a three-necked flask. 15 g of isophorone diisocyanate (IPDI) and 0.1 g of dibutyltin dilaurate catalyst were added in sequence, nitrogen was introduced for protection, and the mixture was reacted at 80° C. for 2 hours. Subsequently, 5 g of dimethylolpropionic acid (DMPA) was added, and the reaction was continued at 70° C. for 3 hours to synthesize a terminal -NCO polyurethane prepolymer, which was then sealed for later use.

[0068] Step S4: 13 g of activated halloysite and 50 g of polyurethane prepolymer were mixed, 100 mL of acetone was added, and ultrasonic dispersion was performed (400 W, 30 minutes) to form a uniform suspension; 200 mL of deionized water containing 5 mL of triethylamine was slowly added dropwise, and 1.3 g of benzoin dimethyl ether was added as a photosensitizer. The mixture was sheared and emulsified at 10,000 rpm for 20 minutes, and the acetone was removed by vacuum distillation (40°C, 10 kPa) to obtain a composite emulsion;

[0069] Step S5: 10 g of pretreated silicon carbide whiskers were immersed in the composite emulsion and stirred for 2 hours. After being taken out, the coating was dried at 80°C for 12 hours to solidify the coating, and then irradiated with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for cross-linking to obtain modified silicon carbide whiskers.

[0070] A method for preparing freeze-thaw resistant concrete for cold region roads comprises the following steps:

[0071] Add Portland cement, kaolin, and modified silicon carbide whiskers into a blender and dry mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue stirring for 8 minutes to mix evenly to obtain a premix;

[0072] Add water reducing agent and water to the premix, and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0073] Example 5

[0074] A freeze-thaw resistant concrete for cold region roads, comprising the following components in parts by weight:

[0075] 100 parts of coarse aggregate (granite crushed stone, particle size 10-20mm, mud content ≤0.5%), 70 parts of fine aggregate (natural river sand, fineness modulus 3.0, mud content ≤1.0%, chloride ion content ≤0.02%), 45 parts of Portland cement (PO 42.5), 40 parts of kaolin, 15 parts of modified silicon carbide whiskers, 0.8 parts of polycarboxylate water reducer (solid content 30%), and 30 parts of water.

[0076] The preparation method of modified silicon carbide whiskers comprises the following steps:

[0077] Step S1: 10 g of silicon carbide whiskers (5-10 μm in diameter, 300-500 μm in length) were spread on the plasma reactor tray, oxygen was introduced (flow rate 50 sccm), and the vacuum was evacuated to 10 -2 Pa, treated with 80W power for 3 minutes to activate the surface; then transferred to a vacuum reactor and reacted with 5mL of acrylic acid vapor at 70℃ and 1kPa for 2 hours to achieve grafting; nitrogen was introduced for cooling after the reaction, and vacuum annealing was performed at 100℃ for 1 hour to eliminate stress, and then ultrasonically dispersed with 200mL of anhydrous ethanol (300W, 15 minutes) and centrifuged (4000rpm, 10 minutes) 3 times, and finally vacuum dried at 60℃ for 12 hours to obtain pretreated whiskers.

[0078] Step S2: 20 g of halloysite nanotubes (diameter 10-30 nm, length 1-5 μm) were added to 200 mL of 3 mol / L hydrochloric acid solution and etched in an 80°C oil bath at 300 rpm with magnetic stirring for 4 hours. After the reaction, the nanotubes were centrifuged (5000 rpm) and repeatedly washed with deionized water until the filtrate had a pH of 7. The solid was vacuum dried at 80°C for 24 hours to obtain activated halloysite with an increased surface hydroxyl density.

[0079] Step S3: 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) was vacuum dried at 110° C. for 2 hours to remove water, then cooled to room temperature and placed in a three-necked flask. 20 g of isophorone diisocyanate (IPDI) and 0.1 g of dibutyltin dilaurate catalyst were added in sequence, nitrogen was introduced for protection, and the mixture was reacted at 80° C. for 2 hours. Subsequently, 5 g of dimethylolpropionic acid (DMPA) was added, and the reaction was continued at 70° C. for 3 hours to synthesize a terminal-NCO polyurethane prepolymer, which was then sealed for later use.

[0080] Step S4: 15 g of activated halloysite and 50 g of polyurethane prepolymer were mixed, 100 mL of acetone was added, and ultrasonic dispersion was performed (400 W, 30 minutes) to form a uniform suspension; 200 mL of deionized water containing 5 mL of triethylamine was slowly added dropwise, and 1.3 g of benzoin dimethyl ether was added as a photosensitizer. The mixture was sheared and emulsified at 10,000 rpm for 20 minutes, and the acetone was removed by vacuum distillation (40°C, 10 kPa) to obtain a composite emulsion;

[0081] Step S5: 10 g of pretreated silicon carbide whiskers were immersed in the composite emulsion and stirred for 2 hours. After being taken out, the coating was dried at 80°C for 12 hours to solidify the coating, and then irradiated with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for cross-linking to obtain modified silicon carbide whiskers.

[0082] A method for preparing freeze-thaw resistant concrete for cold region roads comprises the following steps:

[0083] Add Portland cement, kaolin, and modified silicon carbide whiskers into a blender and dry mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue stirring for 8 minutes to mix evenly to obtain a premix;

[0084] Add water reducing agent and water to the premix, and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0085] Example 6

[0086] A freeze-thaw resistant concrete for cold region roads, comprising the following components in parts by weight:

[0087] 80 parts of coarse aggregate (limestone crushed stone, particle size 10-20mm, mud content ≤0.5%), 60 parts of fine aggregate (machine-made sand, fineness modulus 2.3, mud content ≤1.0%, chloride ion content ≤0.02%), 35 parts of Portland cement (PO 42.5), 30 parts of kaolin, 10 parts of modified silicon carbide whiskers, 0.3 parts of polycarboxylate water reducer (solid content 30%), and 20 parts of water.

[0088] The preparation method of modified silicon carbide whiskers comprises the following steps:

[0089] Step S1: 10 g of silicon carbide whiskers (5-10 μm in diameter, 300-500 μm in length) were spread on the plasma reactor tray, oxygen was introduced (flow rate 50 sccm), and the vacuum was evacuated to 10 -2 Pa, treated with 80W power for 3 minutes to activate the surface; then transferred to a vacuum reactor and reacted with 5mL of acrylic acid vapor at 70℃ and 1kPa for 2 hours to achieve grafting; nitrogen was introduced for cooling after the reaction, and vacuum annealing was performed at 100℃ for 1 hour to eliminate stress, and then ultrasonically dispersed with 200mL of anhydrous ethanol (300W, 15 minutes) and centrifuged (4000rpm, 10 minutes) 3 times, and finally vacuum dried at 60℃ for 12 hours to obtain pretreated whiskers.

[0090] Step S2: 20 g of halloysite nanotubes (diameter 10-30 nm, length 1-5 μm) were added to 200 mL of 3 mol / L hydrochloric acid solution and etched in an 80°C oil bath at 300 rpm with magnetic stirring for 4 hours. After the reaction, the nanotubes were centrifuged (5000 rpm) and repeatedly washed with deionized water until the filtrate had a pH of 7. The solid was vacuum dried at 80°C for 24 hours to obtain activated halloysite with an increased surface hydroxyl density.

[0091] Step S3: 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) was vacuum dried at 110° C. for 2 hours to remove water, then cooled to room temperature and placed in a three-necked flask. 10 g of isophorone diisocyanate (IPDI) and 0.1 g of dibutyltin dilaurate catalyst were added in sequence, nitrogen was introduced for protection, and the mixture was reacted at 80° C. for 2 hours. Subsequently, 5 g of dimethylolpropionic acid (DMPA) was added, and the reaction was continued at 70° C. for 3 hours to synthesize a terminal -NCO polyurethane prepolymer, which was then sealed for later use.

[0092] Step S4: 10 g of activated halloysite and 50 g of polyurethane prepolymer were mixed, 100 mL of acetone was added, and ultrasonic dispersion was performed (400 W, 30 minutes) to form a uniform suspension; 200 mL of deionized water containing 5 mL of triethylamine was slowly added dropwise, and 1.3 g of benzoin dimethyl ether was added as a photosensitizer. The mixture was sheared and emulsified at 10,000 rpm for 20 minutes, and the acetone was removed by vacuum distillation (40°C, 10 kPa) to obtain a composite emulsion;

[0093] Step S5: 10 g of pretreated silicon carbide whiskers were immersed in the composite emulsion and stirred for 2 hours. After being taken out, the coating was dried at 80°C for 12 hours to solidify the coating, and then irradiated with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for cross-linking to obtain modified silicon carbide whiskers.

[0094] A method for preparing freeze-thaw resistant concrete for cold region roads comprises the following steps:

[0095] Add Portland cement, kaolin, and modified silicon carbide whiskers into a blender and dry mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue stirring for 8 minutes to mix evenly to obtain a premix;

[0096] Add water reducing agent and water to the premix, and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0097] Comparative Example 1

[0098] The difference between Control Example 1 and Example 1 is that silicon carbide whiskers are not added to the concrete.

[0099] Comparative Example 2

[0100] The difference between Comparative Example 2 and Example 2 is that in step S4, activated halloysite is not added to the composite emulsion, and the remaining steps are the same.

[0101] Comparative Example 3

[0102] The difference between Comparative Example 3 and Example 2 is that step S1 is omitted, that is, the silicon carbide whiskers are not pretreated.

[0103] Performance testing:

[0104] 1. Freeze-thaw resistance test: 100mm×100mm×100mm concrete cubes, cured for 28 days, were placed in a freeze-thaw chamber maintained at -20°C to 5°C. The freezing phase was maintained at -20°C for 2 hours, and the thawing phase was heated to 5°C for 1 hour, completing a complete freeze-thaw cycle. After each 50 cycles, the specimens were weighed using an electronic balance with an accuracy of 0.01g to calculate the mass loss rate. The dynamic elastic modulus of the specimens was measured using a 54kHz ultrasonic detector. The modulus retention rate was calculated by comparing the initial value to assess the concrete's resistance to damage from repeated freeze-thaw cycles. The test results are shown in Table 1.

[0105] 2. 150 mm × 150 mm × 150 mm cubic specimens were prepared for compressive strength testing. After 28 days of standard curing, the specimens were placed in an electro-hydraulic servo pressure testing machine. During the compressive test, load was applied uniformly at a rate of 0.5 MPa / s until the specimen failed. Three specimens were prepared for each test, and the final results were averaged to ensure data reliability. The test results are shown in Table 1.

[0106] 3. 28-day-cured concrete was processed into cylindrical specimens with a diameter of 100 mm and a thickness of 50 mm. These were then placed in a 6M NaCl solution. A 60V DC voltage was applied across the specimens, and the amount of charge passing through the specimens was continuously monitored over a 6-hour period. The amount of charge was used to evaluate the concrete's resistance to chloride ion penetration. The charge is positively correlated with the chloride ion permeability coefficient, which is calculated using a formula. A smaller value indicates greater resistance to chloride ion penetration. The test results are shown in Table 1.

[0107] Table 1:

[0108]

[0109] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A freeze-thaw resistant concrete for cold region roads, characterized in that: Comprise the following components by weight: 80-100 parts of coarse aggregate, 60-70 parts of fine aggregate, 35-45 parts of Portland cement, 30-40 parts of kaolin, 10-15 parts of modified silicon carbide whiskers, 0.3-0.8 parts of water reducer, and 20-30 parts of water; The preparation method of modified silicon carbide whiskers comprises the following steps: S1, adding the halloysite nanotubes to a hydrochloric acid solution, performing acid activation treatment under heating conditions, and obtaining activated halloysite nanotubes through centrifugal separation, washing, and drying; S2, polytetrahydrofuran diol, isophorone diisocyanate and catalyst are heated to react under nitrogen protection, and then dimethylol propionic acid continues to react to obtain a polyurethane prepolymer; S3, mixing the activated halloysite nanotubes and the polyurethane prepolymer, then adding acetone solvent to uniformly disperse them by ultrasonication, and then adding deionized water containing triethylamine to perform shear emulsification to obtain a composite emulsion; S4, performing surface plasma treatment on the silicon carbide whiskers to obtain plasma-treated silicon carbide whiskers; Plasma-treated silicon carbide whiskers were grafted with acrylic acid vapor, vacuum annealed, ultrasonically dispersed and washed in anhydrous ethanol to obtain pretreated silicon carbide whiskers. The pretreated silicon carbide whiskers are immersed in a composite emulsion, the surface of the plasma-treated silicon carbide whiskers is coated with an emulsion coating, and then placed in an oven for drying and curing, and then subjected to ultraviolet irradiation treatment to obtain modified silicon carbide whiskers.

2. The freeze-thaw resistant concrete for cold region roads according to claim 1, characterized in that: The coarse aggregate is selected from one or more of granite crushed stone, basalt crushed stone and limestone crushed stone.

3. The freeze-thaw resistant concrete for cold region roads according to claim 2, characterized in that: The coarse aggregate has a particle size of 10-20 mm and a mud content of ≤0.5%.

4. The freeze-thaw resistant concrete for cold region roads according to claim 1, characterized in that: The fine aggregate is selected from one or more of natural river sand and machine-made sand.

5. The freeze-thaw resistant concrete for cold region roads according to claim 4, characterized in that: The fine aggregate has a fineness modulus of 2.3-3.0, a mud content of ≤1.0%, and a chloride ion content of ≤0.02%.

6. The freeze-thaw resistant concrete for cold region roads according to claim 1, characterized in that: In the step S2, the mass ratio of polytetrahydrofuran diol to isophorone diisocyanate is 5:1-2.

7. The freeze-thaw resistant concrete for cold region roads according to claim 1, characterized in that: In the step S3, the mass ratio of the polyurethane prepolymer to the activated halloysite nanotubes is 10:2-3.

8. A method for preparing freeze-thaw resistant concrete for cold region roads according to any one of claims 1 to 7, comprising the following steps: Dry-mixing silicate cement, kaolin, and modified silicon carbide whiskers, then adding coarse aggregate and fine aggregate and continuing to stir and mix uniformly to obtain a premix; Add water reducing agent and water to the premix and continue to stir evenly to obtain freeze-thaw resistant concrete.

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