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

Abstract

The invention discloses freeze-thaw resistant concrete for roads in cold regions and a preparation method of the freeze-thaw resistant concrete, and relates to the technical field of concrete. The preparation method comprises the following steps: carrying out dry mixing on the Portland cement, the kaolin and the silicon carbide whiskers, then adding the coarse aggregate and the fine aggregate, continuing to stir and mix uniformly to obtain a premix, then adding the water reducer and the water into the premix, and continuing to stir uniformly to obtain the freeze-thaw resistant concrete. A proper amount of silicon carbide whiskers are added into the mixed soil, the mixed soil has high strength, high elastic modulus and excellent chemical stability, and the freeze-thaw cycle resistance of the concrete can be remarkably improved through the effects of bridging micro-cracks, blocking crack propagation paths, improving pore structures and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and specifically to an anti-freeze-thaw concrete for cold-region highways and a preparation method thereof. Background Art

[0002] Portland cement is a hydraulic cementitious material mainly composed of calcium silicate, which is jointly composed of Portland cement clinker, appropriate amount of gypsum and specified admixtures. Because of its characteristics such as high early strength, fast setting and hardening speed, and good cementing performance, it is widely used as a cementitious material for concrete in highway engineering construction. However, in the field of cold-region highway engineering, concrete structures need to face the severe environmental test of freeze-thaw cycles for a long time, that is, the water in the pores of concrete freezes and expands at low temperatures, and the generated stress will cause repeated damage to the concrete structure. And Portland cement-based concrete itself has obvious defects in anti-freeze-thaw performance. A large number of connected pores are formed during the cement hydration process. These pores are easy to absorb water and become saturated. During freeze-thaw cycles, the stress generated by the freezing and expansion of water in the pores will cause the continuous expansion of microcracks inside the concrete, resulting in the gradual deterioration of the microstructure of the cement stone. Especially when the environmental temperature fluctuates frequently around 0°C, the frequency of freeze-thaw cycles of water increases, and the microcracks will penetrate each other at a faster speed to form macro-cracks, resulting in the destruction of the integrity of the concrete.

[0003] At present, although traditional measures to improve the anti-freeze-thaw performance of concrete (such as adding air-entraining agents, increasing cement dosage, optimizing aggregate gradation, etc.) can delay freeze-thaw damage to a certain extent, there are limitations such as a significant decrease in strength caused by excessive air entrainment, shrinkage and cracking caused by an increase in cement dosage, and the optimization of aggregate gradation being restricted by construction conditions. It is difficult to fundamentally solve the problem of insufficient anti-freeze-thaw performance of cold-region highway concrete. Summary of the Invention

[0004] The purpose of the present invention is to provide one to solve the technical problem of insufficient anti-freeze-thaw performance of cold-region highway concrete proposed in the above background art. The present invention adds an appropriate amount of silicon carbide whiskers to the mixture. It has high strength, high elastic modulus and excellent chemical stability, and can significantly improve the anti-freeze-thaw cycle ability of concrete by bridging microcracks, hindering the crack propagation path, and improving the pore structure.

[0005] To achieve the above purpose, the present invention provides the following technical solutions: An anti-freeze-thaw concrete for cold-region highways, comprising 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 silicon carbide whiskers, 0.3-0.8 parts of water reducer, and 20-30 parts of water.

[0006] In the technical solution of the present invention, coarse aggregates form a mechanical skeleton, and fine aggregates fill voids to optimize the gradation; portland cement serves as the main cementitious material to provide strength, and calcined kaolin refines pores through the pozzolanic effect; silicon carbide whiskers form a three-dimensional network structure in the concrete, which has high strength, high elastic modulus and excellent chemical stability. By bridging microcracks, hindering the crack propagation path, improving the pore structure and other effects, the freeze-thaw cycle resistance of the concrete can be significantly improved; polycarboxylate superplasticizer reduces the water-cement ratio to improve the density. Through the synergistic effect of dense packing of aggregates, pore optimization of fillers and fiber toughening, this system enables the concrete to have good freeze-thaw resistance.

[0007] Preferably, the coarse aggregates are selected from one or more of granite gravel, basalt gravel, and limestone gravel.

[0008] Preferably, the particle size of the coarse aggregates is 10-20 mm, and the mud content is ≤0.5%.

[0009] Preferably, the fine aggregates are selected from one or more of natural river sand and manufactured sand.

[0010] Preferably, the fineness modulus of the fine aggregates is 2.3-3.0, the mud content is ≤1.0%, and the chloride ion content is ≤0.02%.

[0011] Preferably, the silicon carbide whiskers are subjected to a modification treatment, including the following steps: S1. Add halloysite nanotubes to hydrochloric acid solution, and carry out acid activation treatment under heating conditions. After centrifugal separation, washing and drying, activated halloysite nanotubes are obtained; S2. React polytetrahydrofuran diol, isophorone diisocyanate and a catalyst under nitrogen protection by heating, and then continue to react with dimethylolpropionic acid to obtain a polyurethane prepolymer; S3. Mix the activated halloysite nanotubes and the polyurethane prepolymer, then add acetone solvent and disperse evenly by ultrasonic wave, and then add deionized water containing triethylamine for shear emulsification to obtain a composite emulsion; S4. Immerse the silicon carbide whiskers in the composite emulsion to coat the surface of the plasma-treated silicon carbide whiskers with an emulsion coating, then place them in an oven for drying and curing, and then carry out ultraviolet irradiation treatment to obtain modified silicon carbide whiskers.

[0012] In the technical solution of the present invention, in order to further improve the frost resistance of concrete, the silicon carbide whiskers are modified. First, the halloysite nanotubes are subjected to acid activation treatment. The surface is etched by hydrochloric acid solution to expose more active groups, and at the same time, the dispersibility of the nanotubes is improved. Then, polytetrahydrofuran diol and isophorone diisocyanate are used to carry out a polycondensation reaction to synthesize a reactive polyurethane prepolymer. Then, the activated halloysite nanotubes are compounded with the polyurethane prepolymer. The hydroxyl groups on the surface of halloysite react with -NCO on the polyurethane prepolymer to be combined by covalent bonds, improving the bonding strength between the two. Finally, the silicon carbide whiskers are impregnated in the composite emulsion, and after heat curing and ultraviolet irradiation treatment, a nano-enhanced polymer multifunctional coating is coated on the surface of the silicon carbide whiskers. The inner cavity of halloysite can selectively adsorb free water, reducing the content of freezable water in concrete. The polyurethane can form a hydrophobic barrier, increasing the contact angle of the coating, which can reduce the infiltration of moisture in concrete and lower the chloride ion permeability coefficient. In addition, the polyurethane in the coating can play an elastic buffering role. During freeze-thaw cycles, the polyurethane can absorb about the frost heave strain, thus preventing the concrete from being damaged. The nano-enhanced polymer coating coated on the surface of the silicon carbide whiskers endows the fibers with stress transfer ability and water-blocking and water-absorbing properties, thus significantly enhancing the long-term durability of concrete in harsh environments such as freeze-thaw cycles.

[0013] Preferably, in step S2, the mass ratio of polytetrahydrofuran diol to isophorone diisocyanate is 5:1-2.

[0014] Preferably, in step S3, the mass ratio of the polyurethane prepolymer to the activated halloysite nanotubes is 10:2-3.

[0015] Preferably, in step S4, the silicon carbide whiskers are pretreated, including the following steps: The silicon carbide whiskers are subjected to surface plasma treatment to obtain plasma-treated silicon carbide whiskers; The plasma-treated silicon carbide whiskers are subjected to a grafting reaction with acrylic acid vapor, and after vacuum annealing, ultrasonic dispersion and washing in absolute ethanol, the product is obtained.

[0016] In the technical solution of the present invention, as described above, a nano-enhanced polymer coating is coated on the surface of silicon carbide whiskers to improve the freeze-thaw performance of concrete. However, the research team of the present invention found that when the modified silicon carbide whiskers are incorporated into concrete, during the external force stirring and mixing process, a strong frictional force is generated between the materials, and the nano-enhanced polymer coating coated on the surface of the silicon carbide whiskers is easily detached from its surface, thereby reducing its improvement effect on the freeze-thaw resistance of concrete. To further solve this problem, the present invention pre-treats the silicon carbide whiskers, grafts acrylic acid on its surface to make its surface carry -COOH, and uses -COOH to react with -NCO in the polyurethane prepolymer in the nano-enhanced polymer coating to form a covalent bond, thereby bonding the silicon carbide whiskers and the nano-enhanced polymer coating through chemical bonds, greatly improving the bonding strength between the two, avoiding the subsequent detachment of the coating from the surface of the silicon carbide whiskers, maintaining the stability of the combination of the two, and realizing the further improvement effect on the freeze-thaw resistance of concrete.

[0017] A preparation method of freeze-thaw resistant concrete for cold region highways includes the following steps: Dry-mix portland cement, kaolin, and silicon carbide whiskers, and then add coarse aggregate and fine aggregate and continue to stir and mix evenly to obtain a premix; Add a water reducing agent and water to the premix and continue to stir evenly to obtain freeze-thaw resistant concrete.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. The coarse aggregate and the fine aggregate construct a skeleton and optimize the gradation, the cement and the kaolin form a dense matrix, the silicon carbide whiskers bridge the cracks to enhance the toughness, and the water reducing agent reduces the water-binder ratio, and multiple effects synergistically improve the freeze-thaw resistance; 2. After activation, halloysite is compounded with the polyurethane prepolymer to coat the silicon carbide whiskers to form a coating, which enhances the durability of concrete in harsh environments by adsorbing free water, hydrophobic moisture resistance and elastic buffering. 3. The silicon carbide whiskers are pre-treated to graft acrylic acid, and -COOH forms a covalent bond with -NCO in the coating to prevent the coating from falling off during stirring, and stably improves the improvement effect of the freeze-thaw resistance of concrete. Specific embodiments

[0019] The technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] Example 1 A freeze-thaw resistant concrete for cold region highways includes the following components by weight: 95 parts of coarse aggregate (granite crushed stone, particle size 10 - 20 mm, 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 (P.O 42.5), 39 parts of kaolin, 14 parts of silicon carbide whiskers (particle size 5 - 10 μm, length 300 - 500 μm), 0.7 part of polycarboxylate superplasticizer (solid content 30%), 28 parts of water.

[0021] A preparation method of freeze-thaw resistant concrete for cold region highways, comprising the following steps: Add portland cement, kaolin, and silicon carbide whiskers into a mixer and dry mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue to stir for 8 minutes to mix evenly to obtain a premix. Add superplasticizer and water to the premix and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0022] Example 2 A freeze-thaw resistant concrete for cold region highways, comprising the following components by weight: 95 parts of coarse aggregate (granite crushed stone, particle size 10 - 20 mm, 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 (P.O 42.5), 39 parts of kaolin, 14 parts of modified silicon carbide whiskers, 0.7 part of polycarboxylate superplasticizer (solid content 30%), 28 parts of water.

[0023] The preparation method of the modified silicon carbide whiskers comprises the following steps: Step S1: Lay 10 g of silicon carbide whiskers (particle size 5 - 10 μm, length 300 - 500 μm) flat on the plasma reactor tray, introduce oxygen (flow rate 50 sccm) and evacuate to 10 -2 Pa, treat the surface at a power of 80 W for 3 minutes for activation; then transfer to a vacuum reactor and react with 5 mL of acrylic acid vapor at 70 °C and 1 kPa for 2 hours for grafting; after the reaction, introduce nitrogen for cooling, anneal in vacuum at 100 °C for 1 hour to eliminate stress, then ultrasonically disperse with 200 mL of absolute ethanol (300 W, 15 minutes) and centrifuge and wash (4000 rpm, 10 minutes) 3 times, and finally dry in vacuum at 60 °C for 12 hours to obtain pretreated whiskers.

[0024] Step S2: Add 20 g of halloysite nanotubes (tube diameter 10 - 30 nm, length 1 - 5 μm) into 200 mL of 3 mol / L hydrochloric acid solution, and perform etching in an 80°C oil bath with magnetic stirring at 300 rpm for 4 hours; after the reaction, centrifuge and separate (5000 rpm), wash repeatedly with deionized water until the pH of the filtrate is 7, and dry the solid in a vacuum at 80°C for 24 hours to obtain activated halloysite with an increased surface hydroxyl density.

[0025] Step S3: After drying 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) in a vacuum at 110°C for 2 hours to remove water, cool it to room temperature and add it to a three-necked flask. Then, add 18 g of isophorone diisocyanate (IPDI) and 0.1 g of dibutyltin dilaurate catalyst in sequence, introduce nitrogen protection and react at 80°C for 2 hours; subsequently, add 5 g of dimethylolpropionic acid (DMPA) and continue to react at 70°C for 3 hours to synthesize a polyurethane prepolymer with terminal - NCO, and seal it for standby.

[0026] Step S4: Mix 14 g of activated halloysite with 50 g of polyurethane prepolymer, add 100 mL of acetone and disperse it by ultrasonic wave (400 W, 30 minutes) to form a uniform suspension; slowly drop 200 mL of deionized water containing 5 mL of triethylamine, and at the same time add 1.3 g of benzoin dimethyl ether as a photosensitizer, shear and emulsify at 10000 rpm for 20 minutes, and remove acetone by vacuum distillation (40°C, 10 kPa) to obtain a composite emulsion; Step S5: Immerse 10 g of pretreated silicon carbide whiskers in the composite emulsion and stir for 2 hours, take them out and dry at 80°C for 12 hours to cure the coating, and then irradiate with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for crosslinking to obtain modified silicon carbide whiskers.

[0027] A preparation method of freeze - thaw resistant concrete for cold region highways includes the following steps: Add portland cement, kaolin, and modified silicon carbide whiskers into a mixer and dry - mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue to stir for 8 minutes to mix evenly to obtain a premix; Add a water - reducing agent and water to the premix and stir at 200 rpm for 10 minutes to obtain freeze - thaw resistant concrete.

[0028] Example 3 A freeze - thaw resistant concrete for cold region highways includes the following components by weight: 85 parts of coarse aggregate (basalt gravel, particle size 10 - 20 mm, mud content ≤ 0.5%), 62 parts of fine aggregate (manufactured sand, fineness modulus 2.5, mud content ≤ 1.0%, chloride ion content ≤ 0.02%), 38 parts of Portland cement (P.O 42.5), 32 parts of kaolin, 13 parts of modified silicon carbide whiskers, 0.4 part of polycarboxylate superplasticizer (solid content 30%), and 22 parts of water.

[0029] The preparation method of the modified silicon carbide whiskers includes the following steps: Step S1: Lay 10 g of silicon carbide whiskers (particle size 5 - 10 μm, length 300 - 500 μm) flat on the tray of the plasma reactor, introduce oxygen (flow rate 50 sccm) and evacuate to 10 -2 Pa, treat the surface with a power of 80 W for 3 minutes to activate; then transfer to a vacuum reactor, react with 5 mL of acrylic acid vapor at 70 °C and 1 kPa for 2 hours to achieve grafting; after the reaction, introduce nitrogen for cooling, perform vacuum annealing at 100 °C for 1 hour to eliminate stress, then ultrasonically disperse with 200 mL of absolute ethanol (300 W, 15 minutes) and centrifuge and wash (4000 rpm, 10 minutes) 3 times, and finally vacuum dry at 60 °C for 12 hours to obtain pretreated whiskers.

[0030] Step S2: Add 20 g of halloysite nanotubes (tube diameter 10 - 30 nm, length 1 - 5 μm) to 200 mL of 3 mol / L hydrochloric acid solution, and magnetically stir at 300 rpm in an 80 °C oil bath for 4 hours for etching; after the reaction, centrifuge and separate (5000 rpm), wash repeatedly with deionized water until the pH of the filtrate is 7, and vacuum dry the solid at 80 °C for 24 hours to obtain activated halloysite with an increased surface hydroxyl density.

[0031] Step S3: After vacuum drying 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) at 110 °C for 2 hours to remove water, cool to room temperature and add it to a three-necked flask, successively add 13 g of isophorone diisocyanate (IPDI) and 0.1 g of dibutyltin dilaurate catalyst, introduce nitrogen for protection and react at 80 °C for 2 hours; then add 5 g of dimethylolpropionic acid (DMPA), and continue to react at 70 °C for 3 hours to synthesize a polyurethane prepolymer with terminal - NCO, and seal for standby.

[0032] Step S4: Mix 12 g of activated halloysite with 50 g of polyurethane prepolymer, add 100 mL of acetone and ultrasonically disperse (400 W, 30 minutes) to form a uniform suspension; slowly drop 200 mL of deionized water containing 5 mL of triethylamine, and at the same time add 1.3 g of benzoin dimethyl ether as a photosensitizer, shear and emulsify at 10000 rpm for 20 minutes, and remove acetone by vacuum distillation (40 °C, 10 kPa) to obtain a composite emulsion; Step S5: Immerse 10 g of pretreated silicon carbide whiskers in the composite emulsion and stir for 2 hours. After taking them out, dry them at 80 °C for 12 hours to cure the coating, and then irradiate them with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for crosslinking to obtain modified silicon carbide whiskers.

[0033] A preparation method of freeze-thaw resistant concrete for cold region highways includes the following steps: Add portland cement, kaolin, and modified silicon carbide whiskers to a mixer and dry mix them at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue to stir for 8 minutes to mix evenly to obtain a premix. Add a water reducing agent and water to the premix and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0034] Example 4 A freeze-thaw resistant concrete for cold region highways includes the following components by weight: 90 parts of coarse aggregate (limestone gravel, particle size 10 - 20 mm, 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 (P.O 42.5), 35 parts of kaolin, 13 parts of modified silicon carbide whiskers, 0.5 part of polycarboxylate water reducing agent (solid content 30%), and 25 parts of water.

[0035] The preparation method of the modified silicon carbide whiskers includes the following steps: Step S1: Lay 10 g of silicon carbide whiskers (particle size 5 - 10 μm, length 300 - 500 μm) flat on the tray of the plasma reactor, introduce oxygen (flow rate 50 sccm) and evacuate to 10 -2 Pa, treat the surface at a power of 80 W for 3 minutes for activation; then transfer it to a vacuum reactor and react with 5 mL of acrylic acid vapor at 70 °C and 1 kPa for 2 hours for grafting; after the reaction, introduce nitrogen for cooling, perform vacuum annealing at 100 °C for 1 hour to eliminate stress, then ultrasonically disperse it with 200 mL of absolute ethanol (300 W, 15 minutes) and centrifuge and wash it (4000 rpm, 10 minutes) 3 times, and finally vacuum dry it at 60 °C for 12 hours to obtain pretreated whiskers.

[0036] Step S2: Add 20 g of halloysite nanotubes (tube diameter 10 - 30 nm, length 1 - 5 μm) to 200 mL of 3 mol / L hydrochloric acid solution, and magnetically stir at 300 rpm in an 80 °C oil bath for 4 hours for etching; after the reaction, perform centrifugal separation (5000 rpm), repeatedly wash with deionized water until the pH of the filtrate is 7, and vacuum dry the solid at 80 °C for 24 hours to obtain activated halloysite with an increased surface hydroxyl density.

[0037] Step S3: After drying 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) under vacuum at 110 °C for 2 hours to remove water, it was cooled to room temperature and added to a three-necked flask. Then, 15 g of isophorone diisocyanate (IPDI) and 0.1 g of dibutyltin dilaurate catalyst were added successively. Nitrogen was introduced for protection and the reaction was carried out 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 an -NCO-terminated polyurethane prepolymer, which was sealed for standby.

[0038] Step S4: 13 g of activated halloysite was mixed with 50 g of polyurethane prepolymer, and 100 mL of acetone was added for ultrasonic dispersion (400 W, 30 minutes) to form a uniform suspension. 200 mL of deionized water containing 5 mL of triethylamine was slowly added dropwise, and at the same time, 1.3 g of benzoin dimethyl ether was added as a photosensitizer. Shear emulsification was carried out at 10000 rpm for 20 minutes, and acetone was removed by vacuum distillation (40 °C, 10 kPa) to obtain a composite emulsion; Step S5: 10 g of pretreated silicon carbide whiskers were immersed in the composite emulsion and stirred for 2 hours. After taking them out, they were dried at 80 °C for 12 hours to cure the coating, and then irradiated with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for crosslinking to obtain modified silicon carbide whiskers.

[0039] A preparation method of freeze-thaw resistant concrete for cold region highways includes the following steps: Add portland cement, kaolin, and modified silicon carbide whiskers to a mixer and dry mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue to stir for 8 minutes to mix evenly to obtain a premix; Add a water reducing agent and water to the premix and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0040] Example 5 A freeze-thaw resistant concrete for cold region highways includes the following components by weight: Coarse aggregate (granite gravel, particle size 10 - 20 mm, mud content ≤ 0.5%) 100 parts, fine aggregate (natural river sand, fineness modulus 3.0, mud content ≤ 1.0%, chloride ion content ≤ 0.02%) 70 parts, portland cement (P.O 42.5) 45 parts, kaolin 40 parts, modified silicon carbide whiskers 15 parts, polycarboxylate water reducing agent (solid content 30%) 0.8 parts, water 30 parts.

[0041] The preparation method of modified silicon carbide whiskers includes the following steps: Step S1: Spread 10 g of silicon carbide whiskers (particle size 5 - 10 μm, length 300 - 500 μm) on the plasma reactor tray, introduce oxygen (flow rate 50 sccm) and evacuate to 10 -2The whiskers were pretreated as follows: Pa was treated at a power of 80 W for 3 minutes to activate the surface; then it was transferred to a vacuum reactor and grafted with 5 mL of acrylic acid vapor at 70 °C and 1 kPa for 2 hours; after the reaction, nitrogen was introduced for cooling, and vacuum annealing was carried out at 100 °C for 1 hour to eliminate stress. Then, it was ultrasonically dispersed in 200 mL of absolute ethanol (300 W, 15 minutes) and centrifugally washed (4000 rpm, 10 minutes) three times. Finally, it was vacuum dried at 60 °C for 12 hours to obtain the pretreated whiskers.

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

[0043] Step S3: After 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) was vacuum dried at 110 °C for 2 hours to remove water, it was cooled to room temperature and added to 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 reaction was carried out at 80 °C for 2 hours; then 5 g of dimethylolpropionic acid (DMPA) was added, and the reaction was continued at 70 °C for 3 hours to synthesize a polyurethane prepolymer with terminal - NCO, which was sealed for later use.

[0044] Step S4: 15 g of activated halloysite was mixed with 50 g of polyurethane prepolymer, and ultrasonically dispersed in 100 mL of acetone (400 W, 30 minutes) to form a homogeneous suspension; 200 mL of deionized water containing 5 mL of triethylamine was slowly added dropwise, and at the same time, 1.3 g of benzoin dimethyl ether was added as a photosensitizer, and shear emulsification was carried out at 10000 rpm for 20 minutes. Acetone was removed by vacuum distillation (40 °C, 10 kPa) to obtain a composite emulsion; Step S5: 10 g of pretreated silicon carbide whiskers were immersed in the composite emulsion and stirred for 2 hours. After taking them out, they were dried at 80 °C for 12 hours to cure the coating, and then irradiated with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for crosslinking to obtain modified silicon carbide whiskers.

[0045] A preparation method of freeze - thaw resistant concrete for cold region highways includes the following steps: Portland cement, kaolin, and modified silicon carbide whiskers were added to a mixer and dry - mixed at 150 rpm for 5 minutes, then coarse aggregate and fine aggregate were added and stirring was continued for 8 minutes to mix evenly to obtain a premix; A water - reducing agent and water were added to the premix, and stirring was carried out at 200 rpm for 10 minutes to obtain freeze - thaw resistant concrete.

[0046] Example 6 An anti-freeze-thaw concrete for cold-region highways, comprising the following components by weight: 80 parts of coarse aggregate (limestone gravel, particle size 10 - 20 mm, mud content ≤ 0.5%), 60 parts of fine aggregate (manufactured sand, fineness modulus 2.3, mud content ≤ 1.0%, chloride ion content ≤ 0.02%), 35 parts of Portland cement (P.O 42.5), 30 parts of kaolin, 10 parts of modified silicon carbide whiskers, 0.3 part of polycarboxylate water reducer (solid content 30%), and 20 parts of water.

[0047] The preparation method of the modified silicon carbide whiskers comprises the following steps: Step S1: Lay 10 g of silicon carbide whiskers (particle size 5 - 10 μm, length 300 - 500 μm) flat on the plasma reactor tray, introduce oxygen (flow rate 50 sccm) and evacuate to 10 -2 Pa, treat the surface with a power of 80 W for 3 minutes for activation; then transfer to a vacuum reactor, react with 5 mL of acrylic acid vapor at 70 °C and 1 kPa for 2 hours for grafting; after the reaction, introduce nitrogen for cooling, conduct vacuum annealing at 100 °C for 1 hour to eliminate stress, then ultrasonically disperse with 200 mL of absolute ethanol (300 W, 15 minutes) and centrifuge and wash (4000 rpm, 10 minutes) 3 times, and finally conduct vacuum drying at 60 °C for 12 hours to obtain pretreated whiskers.

[0048] Step S2: Add 20 g of halloysite nanotubes (tube diameter 10 - 30 nm, length 1 - 5 μm) to 200 mL of 3 mol / L hydrochloric acid solution, conduct etching with magnetic stirring at 300 rpm in an 80 °C oil bath for 4 hours; after the reaction, centrifuge and separate (5000 rpm), repeatedly wash with deionized water until the pH of the filtrate is 7, and conduct vacuum drying of the solid at 80 °C for 24 hours to obtain activated halloysite with an increased surface hydroxyl density.

[0049] Step S3: After drying 50 g of polytetrahydrofuran diol (PTMG, molecular weight 1000) in vacuum at 110 °C for 2 hours to remove water, cool to room temperature and add it to a three-necked flask, successively add 10 g of isophorone diisocyanate (IPDI) and 0.1 g of dibutyltin dilaurate catalyst, introduce nitrogen for protection and react at 80 °C for 2 hours; then add 5 g of dimethylolpropionic acid (DMPA), continue to react at 70 °C for 3 hours to synthesize a polyurethane prepolymer with terminal -NCO, and seal for standby.

[0050] Step S4: Mix 10 g of activated halloysite with 50 g of polyurethane prepolymer, add 100 mL of acetone and disperse ultrasonically (400 W, 30 minutes) to form a homogeneous suspension; slowly dropwise add 200 mL of deionized water containing 5 mL of triethylamine, and at the same time add 1.3 g of benzoin dimethyl ether as a photosensitizer, shear emulsify at 10,000 rpm for 20 minutes, and remove acetone by vacuum distillation (40 °C, 10 kPa) to obtain a composite emulsion; Step S5: Immerse 10 g of pretreated silicon carbide whiskers in the composite emulsion and stir for 2 hours, take out and dry at 80 °C for 12 hours to cure the coating, and then irradiate with an ultraviolet lamp (365 nm, 100 mW / cm²) for 30 minutes for crosslinking to obtain modified silicon carbide whiskers.

[0051] A preparation method of freeze-thaw resistant concrete for cold region highways includes the following steps: Add portland cement, kaolin, and modified silicon carbide whiskers to a mixer and dry mix at 150 rpm for 5 minutes, then add coarse aggregate and fine aggregate and continue to stir for 8 minutes to mix evenly to obtain a premix; Add a water reducing agent and water to the premix and stir at 200 rpm for 10 minutes to obtain freeze-thaw resistant concrete.

[0052] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that silicon carbide whiskers are not added to the concrete.

[0053] Comparative Example 2 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.

[0054] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that Step S1 is omitted, that is, the silicon carbide whiskers are not pretreated.

[0055] Performance test: 1. Freeze-thaw cycle test: Put 100 mm×100 mm×100 mm concrete cube specimens cured for 28 days into a freeze-thaw cycle box at -20 °C - 5 °C, set the freezing stage to maintain -20 °C and continue for 2 hours, and the melting stage to heat up to 5 °C and maintain for 1 hour to form a complete freeze-thaw cycle. After every 50 cycles are completed, use an electronic balance with a precision of 0.01 g to weigh the mass of the specimens to calculate the mass loss rate, and at the same time use an ultrasonic detector with a frequency of 54 kHz to measure the dynamic elastic modulus of the specimens, and obtain the modulus retention rate by comparing with the initial value to evaluate the anti-damage ability of the concrete in the repeated freeze-thaw environment. The test results are shown in Table 1.

[0056] 2. Prepare 150mm×150mm×150mm cube specimens for compressive strength testing. After 28 days of standard curing, place the specimens in an electro-hydraulic servo pressure testing machine. During the compressive test, load uniformly at a rate of 0.5 MPa / s until the specimens are damaged. Prepare 3 specimens for each group of tests, and take the average of the final results to ensure data reliability. The test results are shown in Table 1.

[0057] 3. Process the concrete cured for 28 days into cylindrical specimens with a diameter of 100 mm and a thickness of 50 mm, and place them in 6M NaCl solution. Apply a 60V DC voltage on both sides of the specimens, and continuously monitor the charge passing through the specimens within 6 hours. Evaluate the chloride ion penetration resistance of the concrete according to the amount of charge. The amount of charge is positively correlated with the chloride ion penetration coefficient, and the penetration coefficient value is obtained through formula conversion. The smaller this value is, the stronger the ability of the concrete to resist chloride ion intrusion. The test results are shown in Table 1.

[0058] Table 1: Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An anti-freeze-thaw concrete for cold-region highways, characterized in that, It includes the following components by weight parts: 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 reducing agent, and 20 - 30 parts of water.

2. The anti-freezing and thawing concrete for cold region highways according to claim 1, wherein The coarse aggregate is selected from one or more of granite gravel, basalt gravel, and limestone gravel.

3. The anti-freezing and thawing concrete for cold region highways according to claim 2, wherein, The particle size of the coarse aggregate is 10 - 20mm, and the mud content is ≤0.5%.

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

5. The anti-freezing and thawing concrete for cold region highways according to claim 4, wherein The fineness modulus of the fine aggregate is 2.3 - 3.0, the mud content is ≤1.0%, and the chloride ion content is ≤0.02%.

6. The anti-freezing and thawing concrete for cold region highways according to claim 1, characterized in that, The silicon carbide whiskers are subjected to modification treatment, including the following steps: S1. Add halloysite nanotubes to hydrochloric acid solution, carry out acid activation treatment under heating conditions, and obtain activated halloysite nanotubes through centrifugal separation, washing, and drying. S2. Heat and react polytetrahydrofuran diol, isophorone diisocyanate, and a catalyst under nitrogen protection, and then continue to react with dimethylolpropionic acid to obtain a polyurethane prepolymer. S3. Mix the activated halloysite nanotubes and the polyurethane prepolymer, then add acetone solvent and disperse evenly by ultrasonic treatment, and then add deionized water containing triethylamine for shear emulsification to obtain a composite emulsion. S4. Immerse the silicon carbide whiskers in the composite emulsion to coat the surface of the plasma-treated silicon carbide whiskers with an emulsion coating, then place them in an oven for drying and curing, and then carry out ultraviolet light irradiation treatment to obtain modified silicon carbide whiskers.

7. The anti-freezing and thawing concrete for cold region highways according to claim 6, wherein In step S2, the mass ratio of polytetrahydrofuran diol to isophorone diisocyanate is 5:1 - 2.

8. The anti-freezing and thawing concrete for cold region highways according to claim 6, characterized in that, In step S3, the mass ratio of the polyurethane prepolymer to the activated halloysite nanotubes is 10:2 - 3.

9. A frost-resistant and thaw-resistant concrete for cold-region highways according to claim 6, characterized in that, In step S4, the silicon carbide whiskers are pre-treated, including the following steps: Carry out surface plasma treatment on the silicon carbide whiskers to obtain plasma-treated silicon carbide whiskers. Carry out a graft reaction between the plasma-treated silicon carbide whiskers and acrylic vapor, and then carry out vacuum annealing, ultrasonic dispersion in anhydrous ethanol, and washing to obtain the product.

10. A preparation method of freeze-thaw resistant concrete for cold region highways as described in any one of claims 1 - 9, including the following steps: Dry mix the portland cement, kaolin, and silicon carbide whiskers, and then add the coarse aggregate and fine aggregate and continue to stir and mix evenly to obtain a premix. Add the water reducing agent and water to the premix and continue to stir evenly to obtain freeze-thaw resistant concrete.

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