Low-temperature freeze-proof and crack-resistant concrete and preparation method thereof

Abstract

This invention discloses a low-temperature antifreeze and crack-resistant concrete and its preparation method, belonging to the field of concrete technology. The concrete comprises the following components: cementitious materials, sand, crushed stone, temperature-responsive modified bamboo aggregate, water-reducing agent, water, succinic anhydride, fucoidan, and rock wool fiber. The preparation method of the temperature-responsive modified bamboo aggregate is as follows: S1. N-isopropylacrylamide and dodecyl acrylate are dissolved in a solvent, and initiator one is added to carry out a polymerization reaction. After separation, a copolymer of N-isopropylacrylamide monomer is obtained; S2. The copolymer of N-isopropylacrylamide monomer is dissolved in a calcium citrate aqueous solution and stirred evenly to obtain a copolymer of N-isopropylacrylamide aqueous solution; S3. Bamboo aggregate, copolymer of N-isopropylacrylamide aqueous solution, crosslinking agent, and initiator two are mixed and reacted at 40-50℃ for 4-5 hours to obtain the final product. This invention improves the low-temperature crack resistance of concrete through the synergistic effect of succinic anhydride, fucoidan, temperature-responsive modified bamboo aggregate, and rock wool fiber.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to a low-temperature antifreeze and crack-resistant concrete and its preparation method. Background Technology

[0002] my country's JGJ / T 104-2011 "Code for Winter Construction of Building Engineering" specifies requirements for concrete construction in winter. The process for concrete in winter differs from that of concrete under conventional conditions in all stages, from mix design to pouring, molding, curing, demolding, and use. This is primarily because low temperatures significantly impact the formation of concrete's microstructure and performance development. my country has a vast territory with significant latitudinal differences, with approximately 60% of its area being cold or frigid. These cold regions require extensive winter construction projects, which severely shorten the actual construction period due to the climate. Many major projects even span two to three winter construction periods. The significant reduction in concrete structural strength and durability caused by early frost damage leads to substantial building destruction and economic losses. Therefore, preventing concrete from freezing and cracking at low temperatures has significant engineering application value.

[0003] After concrete is poured, the temperature difference between the concrete and its surrounding environment leads to heat exchange. This is especially true when the concrete is in a sub-zero environment. Through this heat exchange, the stability of the freshly mixed concrete decreases. The large amount of free water remaining inside the concrete at sub-zero temperatures will generate high frost heave stress upon freezing, leading to concrete failure. In general, scholars from various countries have conducted extensive research on the mechanism of concrete frost damage and proposed numerous theories, such as the hydrostatic pressure theory, the osmotic pressure theory, the adsorbed water theory, and the theory of concrete aggregate frost expansion. The hydrostatic pressure theory posits that the pressure caused by freezing expansion forces capillary water inside the concrete and moisture from the external environment to migrate to areas with lower saturation. When concrete has high permeability, a water pressure gradient is formed, exerting pressure on the pore walls. As the cooling rate increases, the water saturation in the capillaries increases and the pore size decreases, leading to increased water pressure. When the water pressure exceeds the tensile strength of the concrete, the pore walls rupture, causing the concrete to crack due to frost heave. The theory of concrete aggregate frost heave suggests that when aggregates in concrete absorb water and freeze at low temperatures, the volume of ice increases by approximately 9% compared to water. The water in the aggregate expands due to freezing, causing internal stress and volume changes. Since the aggregate is relatively rigid, this ultimately leads to aggregate cracking or detachment of the interface between the aggregate and the cement paste. Cracks then propagate from the inside, resulting in surface cracking and structural damage to the concrete.

[0004] To improve the antifreeze and crack resistance of concrete, existing technologies mainly focus on the following aspects: (1) Adding antifreeze air-entraining agents to improve the antifreeze performance of concrete, but this can easily have an adverse effect on the strength and durability of concrete; (2) Improving the impermeability of concrete and reducing the migration of external moisture into the interior, but the effect of improving the density of concrete is limited, and there is a large amount of unhydrated free water in the concrete mixing, molding and hydration process, which will still produce a frost heave effect under low temperature conditions; (3) Introducing fiber anti-cracking reinforcing materials such as polypropylene fiber or polyvinyl alcohol fiber, but this only plays an anti-cracking role and has no significant effect on improving the early hydration effect of reinforced concrete in low temperature environment.

[0005] Based on the above analysis, improving the low-temperature freeze-thaw resistance and crack prevention performance of concrete requires systematic and multi-faceted optimization of concrete material design. This includes increasing the density of the concrete's interior and surface, enhancing its early strength and impermeability to prevent external moisture from penetrating and freezing, and reducing moisture in the concrete capillaries while ensuring the cementitious hydration effect, thereby weakening the rigid expansion and damage of aggregates. Only in this way can the freeze-thaw resistance and crack prevention performance of concrete be optimized, thereby improving the safety of engineering structures and extending their service life. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, one of the objectives of this invention is to provide a low-temperature antifreeze and crack-resistant concrete. Through the synergistic effect of various components, the low-temperature antifreeze performance of concrete for winter construction is improved in four aspects: enhanced cement activity, self-insulation, water absorption and toughening of concrete aggregate in response to temperature drop, and increased capillary water setting point. This results in concrete with excellent low-temperature crack resistance and structural durability, solving the problems of low strength and easy frost heave and cracking of traditional concrete in low-temperature winter environments.

[0007] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0008] A low-temperature antifreeze and crack-resistant concrete, the raw materials of which include the following components: cementitious materials, sand, crushed stone, temperature-responsive modified bamboo aggregate, water-reducing agent, water, succinic anhydride, fucoidan, and rock wool fiber.

[0009] The preparation method of the temperature-responsive modified bamboo aggregate includes the following steps:

[0010] S1. N-Isopropylacrylamide and dodecyl acrylate are dissolved in a solvent, initiator one is added, and polymerization reaction is carried out under an inert gas atmosphere. After precipitation, separation and drying, the copolymerized N-isopropylacrylamide monomer is obtained.

[0011] S2. Dissolve the copolymer N-isopropylacrylamide monomer obtained in step S1 in an aqueous solution of calcium citrate, and stir until homogeneous to obtain an aqueous solution of copolymer N-isopropylacrylamide;

[0012] S3. Mix bamboo aggregate, aqueous solution of N-isopropylacrylamide copolymer, crosslinking agent and initiator II, and react at 40-50℃ for 4-5 hours to obtain the temperature-responsive modified bamboo aggregate.

[0013] In the above technical solution, N-isopropylacrylamide is a temperature-responsive, reversible polymer. Its macromolecular chain simultaneously possesses hydrophilic amide groups and hydrophobic isopropyl groups, allowing for a phase transition with temperature changes. When the temperature is below the critical dissolution temperature, the amide groups in N-isopropylacrylamide exhibit strong hydrogen bonding with surrounding water molecules, resulting in a hydrophilic polymer with an extended molecular chain. When the temperature is above the critical dissolution temperature, the hydrophobic interactions between the isopropyl molecules in N-isopropylacrylamide intensify, leading to a hydrophobic polymer with a tightly packed granular structure.

[0014] The critical dissolution temperature of conventional N-isopropylacrylamide is generally between 30 and 35°C. Dodecyl acrylate is a hydrophobic monomer with a long-chain alkyl group. Compared to the shorter alkyl chain of butyl acrylate, the long-chain alkyl group of dodecyl acrylate contributes to the formation of a more hydrophobic network in the polymer. This invention introduces the long-chain alkyl group of dodecyl acrylate into the polymer through copolymerization, reducing its interaction with water and providing more hydrophobic components. As the temperature increases, the molecular motion of the polymer intensifies. Because the copolymerized N-isopropylacrylamide has more hydrophobic components, its hydrogen bonds with water molecules break more easily and earlier (i.e., compared to N-isopropylacrylamide, the breaking of hydrogen bonds in copolymerized N-isopropylacrylamide requires less heat energy), thus achieving a reduction in the critical dissolution temperature. Simultaneously, this invention introduces calcium citrate into the aqueous solution of copolymerized N-isopropylacrylamide. The calcium ions in calcium citrate interact with water molecules through an ion-shielding effect, weakening the hydrogen bonding structure between water molecules. The citrate ions themselves can compete with the hydrogen bonds between water molecules, thereby further lowering the critical dissolution temperature of the copolymerized N-isopropylacrylamide. Through these two aspects, the hydrophilic-hydrophobic transition temperature of the aqueous solution of copolymerized N-isopropylacrylamide is adjusted to 5-10℃.

[0015] Copolymerized N-isopropylacrylamide can undergo physical state changes such as swelling and gelation with temperature changes, but its structure is relatively loose and unstable and easily affected by environmental factors. This invention introduces crosslinking agents and initiators to prepare temperature-responsive modified bamboo aggregate by copolymerization. On the one hand, it can effectively enhance the structural stability and physical properties of the temperature-responsive monomer gel. On the other hand, it can enable the temperature-responsive monomer gel to form a good crosslinking structure with the natural fibers on the surface of bamboo aggregate, improve the toughness of bamboo aggregate, strengthen the adhesion between the gel and the surface of bamboo aggregate, and enhance the frost resistance of bamboo aggregate.

[0016] Bamboo is lightweight, hygroscopic, and highly tough. Adding bamboo aggregate to concrete effectively improves its toughness, impact resistance, and crack resistance. Temperature-responsive modified bamboo aggregate, coated with copolymer N-isopropylacrylamide, initially prevents water absorption during cement hydration, as the concrete remains at a relatively high temperature. The modified bamboo aggregate, being hydrophobic, does not affect normal hydration and avoids the influence of organic matter in the bamboo aggregate on the cement paste hydration process. As the external temperature decreases and cement hydration weakens, the internal temperature drops further. The copolymer N-isopropylacrylamide gradually becomes hydrophilic, absorbing excess water from the concrete capillaries. The water entering the bamboo aggregate freezes at low temperatures, increasing in volume. However, the high toughness of the bamboo aggregate prevents significant rigid expansion of the cementitious base, effectively addressing the cracking problem caused by frost heave and significantly improving the crack resistance of concrete at low temperatures. As the ambient temperature rises and the frozen moisture in the bamboo aggregate melts, it can have an internal curing effect, further improving the later strength of the concrete.

[0017] Succinic anhydride contains readily reactive anhydride groups (-C=O), which readily hydrolyze in moist or alkaline environments to form succinic acid. On one hand, the hydrolyzed succinic acid acts as a surfactant, effectively reducing the surface tension of cement particles, promoting better contact and dispersion between cement particles and water, accelerating the hydration reaction, and enhancing the early strength of concrete. On the other hand, the carboxyl groups (-COOH) in succinic acid can react with free calcium ions produced during hydration and calcium ions from calcium citrate (precipitated in modified bamboo aggregate) to form calcium succinate. This calcium succinate fills the cement-based interface and pores, promoting the cement hydration reaction, improving the early strength and density of concrete, and enhancing its resistance to external moisture penetration.

[0018] Fucoidan possesses superior water retention, gelling, and polymer properties, with its molecular chains densely packed with hydroxyl (-OH) and sulfate ester (-SO3) groups. -Fucoidan can form stable hydrogen bonds with water molecules, lowering the freezing point of aqueous solutions in concrete, slowing down the growth rate of capillary water ice crystals inside the concrete, and improving the frost resistance of concrete. Fucoidan gels upon contact with water, but this gelation is reversible; when the pH or calcium ion concentration is low, the gel remains dissolved. When fucoidan is added to concrete during mixing, the pH and calcium ion concentration are relatively low, allowing fucoidan to effectively disperse without affecting the mixing and workability of the concrete. As the degree of hydration increases, the pH and calcium ion concentration of the concrete increase significantly. Fucoidan forms a tortuous, flexible, and dense three-dimensional network structure within the concrete capillary channels. On one hand, it "fixes" excess water within the concrete channels, reducing the free flow of water and weakening the migration of frozen water ice crystals to weak interfaces in the cementitious matrix. On the other hand, it imparts elasticity and toughness to the concrete channels, disperses and absorbs stress caused by freezing expansion, and improves the density and structural stability of the concrete, enhancing its impermeability.

[0019] By adopting the above technical solution, the concrete of this invention forms a three-tiered defense against freezing and cracking through the synergistic effect of its components, comprehensively improving the low-temperature freezing resistance of concrete. Firstly, the cement-based active strengthening effect of succinic anhydride and the thermal insulation and toughening effect of rock wool fiber effectively improve the density, resistance to external moisture penetration, and crack resistance of the concrete, serving as the first line of defense against freezing and cracking. Secondly, temperature-responsive modified bamboo aggregate absorbs excess free water in the capillaries, and the toughness of the bamboo aggregate reduces rigid expansion, effectively solving the problem of freezing expansion caused by residual capillary moisture and moisture in the aggregate, thus serving as the second line of defense against freezing and cracking. Finally, for the remaining moisture in the capillaries after absorption by the temperature-responsive modified bamboo aggregate, fucoidan is used to lower the freezing point of the remaining moisture, reducing free flow of moisture and simultaneously enhancing the elasticity and toughness of the concrete capillaries, effectively weakening the freezing expansion effect of free water in the capillaries (both from the concrete itself and from external penetration), serving as the third line of defense against freezing and cracking.

[0020] Preferably, the molar ratio of N-isopropylacrylamide to dodecyl acrylate is (5~5.5):1.

[0021] Preferably, the polymerization reaction is carried out at a temperature of 70-80°C for 3-5 hours.

[0022] Preferably, the mass ratio of the N-isopropylacrylamide monomer, calcium citrate, and water is 1:(0.1~0.2):5.

[0023] Preferably, the initiator one and the initiator two are ammonium persulfate or potassium persulfate, the mass of the initiator one is 0.8% to 1.0% of the mass of N-isopropylacrylamide, and the mass of the initiator two is 1.0% to 1.5% of the mass of the copolymerized N-isopropylacrylamide monomer.

[0024] Preferably, the crosslinking agent is N,N'-methylenebisacrylamide, and the mass of the crosslinking agent is 0.2% to 0.4% of the mass of the copolymerized N-isopropylacrylamide monomer.

[0025] Preferably, the method for preparing the bamboo aggregate is as follows: mature moso bamboo is crushed into bamboo particles, and after sieving, bamboo aggregate raw materials with a size of 5-15 mm in length, 5-10 mm in width, and 2-3 mm in thickness are obtained, and then dried to obtain the bamboo aggregate.

[0026] Preferably, the rock wool fiber density is 20~40 kg / m³. 3 Thermal conductivity 0.030~0.045 W / (m•K), tensile strength ≥100 kPa.

[0027] Preferably, before use, the rock wool fiber is soaked in a styrene-acrylic copolymer emulsion containing vitrified microspheres, stirred evenly, and then dried.

[0028] Rock wool fibers in concrete act as bridging agents, disperse stress, improve concrete toughness, reduce cracks caused by temperature or load changes, and enhance the low-temperature crack resistance of concrete. Furthermore, rock wool fibers possess excellent thermal insulation properties, effectively improving the thermal insulation performance of concrete, reducing heat conduction, and significantly slowing down the temperature drop caused by low-temperature environments, thus maintaining the temperature required for normal cement hydration. However, rock wool fibers have drawbacks such as high brittleness and strong water absorption; they are prone to breakage at low temperatures, easily agglomerate or settle in concrete, and absorb excessive moisture, affecting cement hydration and their own thermal insulation performance. Encapsulating rock wool fibers with a styrene-acrylic copolymer emulsion forms a flexible film on the fiber surface, enhancing elasticity and toughness, reducing moisture absorption, and optimizing the thermal insulation performance of rock wool fibers. Vitrified microspheres are granular with irregular and rough surfaces, which can improve the surface roughness of rock wool fibers encapsulated in copolymer emulsions, enhance the adhesion between modified rock wool fibers and cement-based materials, optimize the interfacial transition zone, and at the same time, they have very low thermal conductivity, which can further enhance the thermal insulation performance of rock wool fibers and reduce heat transfer.

[0029] More preferably, the styrene-acrylic acid copolymer emulsion has a solid content of 40%~50% and a viscosity of 500~1000 mPa•s; the vitrified microspheres have a particle size of 60~70 mesh and a thermal conductivity (25℃) ≤0.070 W / (m•K).

[0030] Preferably, the concrete comprises the following components by weight: 413-486 parts of cementitious material, 710-750 parts of sand, 900-930 parts of crushed stone, 130-160 parts of temperature-responsive modified bamboo aggregate, 5-8 parts of water-reducing agent, 145-155 parts of water, 5-8 parts of succinic anhydride, 1-2 parts of fucoidan, and 2-3 parts of rock wool fiber.

[0031] More preferably, the cementitious material comprises cement, fly ash, granulated blast furnace slag and silica fume in a mass ratio of (300~340):(60~80):(50~60):(3~6).

[0032] Another object of the present invention is to provide a method for preparing the aforementioned low-temperature antifreeze and crack-resistant concrete, characterized by comprising the following steps:

[0033] The sand, gravel, and cementitious materials are mixed evenly. Then, 2 / 4 water-reducing agent and 2 / 4 water are added and mixed evenly. Next, the temperature-responsive modified bamboo aggregate, rock wool fiber, succinic anhydride, 1 / 4 water-reducing agent, and 1 / 4 water are added and mixed evenly. Finally, fucoidan, 1 / 4 water-reducing agent, and 1 / 4 water are added and mixed evenly to obtain concrete paste.

[0034] Compared with the prior art, the advantages of the present invention are:

[0035] (1) This invention forms three lines of defense for concrete to resist freezing and cracking at low temperatures by using succinic anhydride, rock wool fiber, temperature-responsive modified bamboo aggregate and fucoidan gum. It synergistically improves the low-temperature antifreeze performance of concrete in winter construction from four aspects: cement activity enhancement and self-insulation, temperature-responsive water absorption and toughening of modified bamboo aggregate, and capillary water freezing point enhancement. This solves the problem of low strength and easy freezing and cracking of traditional concrete in low-temperature winter environments.

[0036] (2) The present invention adds temperature-responsive modified bamboo aggregate to concrete. In the early stage of hydration, the temperature-responsive modified bamboo aggregate does not absorb water in the concrete and does not affect the normal hydration and workability of the concrete. When the external ambient temperature continues to decrease and the cement hydration weakens, the internal temperature of the concrete continues to drop. It can absorb excess water in the capillary pores of the concrete and reduce the influence of the expansion stress of water freezing in the capillary pores. As bamboo aggregate has high toughness, when the water entering the bamboo aggregate freezes at low temperature and the volume increases, it will not cause a large rigid expansion of the cement base. This solves the problem of concrete cracking caused by aggregate freezing expansion and significantly improves the crack resistance of concrete at low temperature. In addition, after the ambient temperature warms up and the temperature rises, the bamboo aggregate can also play an internal curing role.

[0037] (3) This invention utilizes styrene-acrylic copolymer emulsion and vitrified microspheres to modify rock wool fibers, effectively improving the elasticity and toughness of the rock wool fibers, overcoming their shortcomings of high brittleness and strong water absorption, strengthening the thermal insulation performance of the rock wool fibers, and enhancing the adhesion between the modified rock wool fibers and the cement base. Utilizing the good fiber toughness of rock wool fibers reduces cracks caused by temperature or load changes, improving the low-temperature crack resistance of concrete. More importantly, it effectively improves the thermal insulation performance of concrete, reduces heat conduction, significantly slows down the temperature drop inside the concrete caused by the low-temperature environment, and maintains the temperature required for normal cement hydration.

[0038] (4) This invention utilizes succinic anhydride to promote better contact and dispersion of cement particles with water, accelerate the hydration reaction, and simultaneously generate calcium succinate with calcium ions, filling the cement-based interface and pore voids, thereby improving the early strength and density of concrete. Fucoidan lowers the freezing point of the aqueous solution in concrete without affecting the mixing and workability of the concrete, and can form a three-dimensional network structure within the capillary pores of the concrete, "fixing" excess water and dispersing and absorbing stress caused by freezing expansion. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] The low-temperature antifreeze and crack-resistant concrete of the present invention comprises the following components in parts by weight: 413-486 parts of cementitious material, 710-750 parts of sand, 900-930 parts of crushed stone, 130-160 parts of temperature-responsive modified bamboo aggregate, 5-8 parts of water-reducing agent, 145-155 parts of water, 5-8 parts of succinic anhydride, 1-2 parts of fucoidan, and 2-3 parts of rock wool fiber.

[0041] The cementitious materials include cement, fly ash, granulated blast furnace slag and silica fume in a mass ratio of (300~340):(60~80):(50~60):(3~6).

[0042] In the following examples and comparative examples, the cement is ordinary Portland cement P•O 52.5; the sand can be natural river sand and / or manufactured sand, and when it is a mixture of natural river sand and manufactured sand, the mass ratio of manufactured sand to natural river sand is (2~3):(7~8), the fineness modulus of the natural sand is 2.8~3.2, the fineness modulus of the manufactured sand is 2.7~3.0, and the stone powder content is less than 10%; the crushed stone is limestone crushed stone aggregate with a particle size of 10~25mm and an apparent density of 2600~2700kg / m³. 3Crushing value ≤20%; water-reducing agent is polycarboxylate superplasticizer, with a water reduction rate of 22~28%. Rock wool fiber density 20~40 kg / m³. 3 Thermal conductivity 0.030~0.045 W / (m•K), tensile strength ≥100 kPa; solid content of styrene-acrylic copolymer emulsion 40%~50%, viscosity 500~1000 mPa•s; vitrified microspheres with a particle size of 60~70 mesh and thermal conductivity (25℃) ≤0.070 W / (m•K).

[0043] N-Isopropylacrylamide, chemically pure, Shanghai Aladdin Biochemical Technology Co., Ltd.; Ammonium persulfate (APS), analytical grade, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0044] The preparation method of bamboo aggregate is as follows: mature moso bamboo is crushed into bamboo particles, and then the particles are screened by vibration to obtain bamboo aggregate raw materials with a length of 5~15mm, a width of 5~10mm and a thickness of 2~3mm. The bamboo aggregate raw materials are then dried in a ventilated environment at 65~85℃ to obtain bamboo aggregate.

[0045] Example 1

[0046] This embodiment provides a low-temperature antifreeze and crack-resistant concrete, comprising the following components in parts by weight: 300 parts cement, 60 parts fly ash, 60 parts granulated blast furnace slag, 6 parts silica fume, 750 parts sand, 900 parts crushed stone, 160 parts temperature-responsive modified bamboo aggregate, 5 parts water-reducing agent, 155 parts water, 8 parts succinic anhydride, 2 parts fucoidan, and 3 parts modified rock wool fiber.

[0047] The preparation method of temperature-responsive modified bamboo aggregate is as follows:

[0048] S1. Analytical grade N-isopropylacrylamide and dodecyl acrylate were dissolved in dimethyl sulfoxide solvent at a molar ratio of 5:1 to obtain a mixture with the concentration of N-isopropylacrylamide of 1.2 mol / L. Then, 1% by mass of ammonium persulfate of N-isopropylacrylamide was added, and the mixture was stirred and the polymerization reaction was carried out at 80°C under nitrogen protection for 3 hours until the monomers were completely reacted. The solution was poured into a large amount of cold ethanol for precipitation for 4 hours. After filtration and washing with ethanol to remove unreacted monomers, the copolymerized N-isopropylacrylamide monomer was obtained after drying.

[0049] S2. Mix the copolymer N-isopropylacrylamide monomer, calcium citrate and water in a mass ratio of 1:0.2:5 and stir evenly at 15°C to obtain an aqueous solution of copolymer N-isopropylacrylamide.

[0050] S3. Add bamboo aggregate (the mass of bamboo aggregate is 12% of the mass of the aqueous solution of N-isopropylacrylamide) to the aqueous solution of N-isopropylacrylamide, then add 0.4% N,N'-methylenebisacrylamide by mass of N-isopropylacrylamide monomer and 1.5% ammonium persulfate by mass of N-isopropylacrylamide monomer, stir evenly, and stir and react at 50°C for 4 hours to obtain temperature-responsive modified bamboo aggregate;

[0051] The preparation method of modified rock wool fiber is as follows: the rock wool fiber is rinsed with deionized water, dried, and then soaked in a styrene-acrylic copolymer emulsion containing vitrified microspheres at a dosage of 8%. The mixture is stirred at 5200 rpm for 8 minutes, then dried at 100℃ for 1 hour to ensure that the emulsion is cured and adhered to the surface of the rock wool fiber.

[0052] The preparation method of low-temperature antifreeze and crack-resistant concrete in this embodiment is as follows:

[0053] M1. Weigh each component according to the parts by weight;

[0054] M2. Mix sand, crushed stone, cement, fly ash, granulated blast furnace slag, and silica fume evenly. Add 2 / 4 water-reducing agent and 2 / 4 water, mix evenly, then add temperature-responsive modified bamboo aggregate, modified rock wool fiber, succinic anhydride, 1 / 4 water-reducing agent, and 1 / 4 water, mix evenly, then add fucoidan, the remaining 1 / 4 water-reducing agent, and 1 / 4 water, mix evenly to obtain concrete paste.

[0055] Example 2

[0056] This embodiment provides a low-temperature antifreeze and crack-resistant concrete, comprising the following components in parts by weight: 340 parts cement, 80 parts fly ash, 50 parts granulated blast furnace slag, 3 parts silica fume, 710 parts sand, 930 parts crushed stone, 130 parts temperature-responsive modified bamboo aggregate, 8 parts water-reducing agent, 145 parts water, 5 parts succinic anhydride, 1 part fucoidan, and 2 parts modified rock wool fiber.

[0057] The preparation method of temperature-responsive modified bamboo aggregate is as follows:

[0058] S1. Analytical grade N-isopropylacrylamide and dodecyl acrylate were dissolved in dimethyl sulfoxide solvent at a molar ratio of 5.5:1 to obtain a mixture with the concentration of N-isopropylacrylamide of 1.4 mol / L. Then, 0.8% by mass of ammonium persulfate of N-isopropylacrylamide was added, and the mixture was stirred and the polymerization reaction was carried out at 70°C under nitrogen protection for 5 h until the monomers were completely reacted. The solution was poured into a large amount of cold ethanol for precipitation for 2 h. After filtration and washing with ethanol to remove unreacted monomers, the copolymerized N-isopropylacrylamide monomer was obtained after drying.

[0059] S2. The copolymer N-isopropylacrylamide monomer, calcium citrate and water are mixed in a mass ratio of 1:0.1:5 and stirred evenly at 10°C to obtain an aqueous solution of copolymer N-isopropylacrylamide.

[0060] S3. Add bamboo aggregate (the mass of bamboo aggregate is 10% of the mass of the aqueous solution of N-isopropylacrylamide) to the aqueous solution of N-isopropylacrylamide, then add 0.2% N,N'-methylenebisacrylamide by mass of N-isopropylacrylamide monomer and 1.0% ammonium persulfate by mass of N-isopropylacrylamide monomer, stir evenly, and stir and react at 40℃ for 5h to obtain temperature-responsive modified bamboo aggregate.

[0061] The preparation method of modified rock wool fiber is as follows: the rock wool fiber is rinsed with deionized water, dried, and then soaked in a styrene-acrylic copolymer emulsion containing vitrified microspheres at a dosage of 10%. The mixture is stirred at 4000 rpm for 15 minutes, then dried at 80°C for 2 hours to ensure that the emulsion is cured and adhered to the surface of the rock wool fiber.

[0062] The preparation method of the low-temperature antifreeze and crack-resistant concrete in this embodiment is the same as that in Embodiment 1.

[0063] Example 3

[0064] The low-temperature antifreeze and crack-resistant concrete in this embodiment is basically the same as that in Embodiment 1, except that unmodified rock wool fiber is used in this embodiment.

[0065] The preparation method of low-temperature antifreeze and crack-resistant concrete in this embodiment is as follows:

[0066] M1. Weigh each component according to the parts by weight;

[0067] M2. Mix sand, crushed stone, cement, fly ash, granulated blast furnace slag, and silica fume evenly. Add 2 / 4 water-reducing agent and 2 / 4 water, mix evenly, then add temperature-responsive modified bamboo aggregate, rock wool fiber, succinic anhydride, 1 / 4 water-reducing agent, and 1 / 4 water, mix evenly, then add fucoidan, the remaining 1 / 4 water-reducing agent, and 1 / 4 water, mix evenly to obtain concrete paste.

[0068] Comparative Example 1

[0069] The concrete in this comparative example is basically the same as that in Example 1, except that bamboo aggregate is used instead of temperature-responsive modified bamboo aggregate in this comparative example, while the amount remains the same.

[0070] Comparative Example 2

[0071] The concrete in this comparative example is basically the same as that in Example 1, except that butyl acrylate is used instead of dodecyl acrylate when preparing the temperature-responsive modified bamboo aggregate in this comparative example.

[0072] Comparative Example 3

[0073] The concrete in this comparative example is basically the same as that in Example 1. The difference is that when preparing the temperature-responsive modified bamboo aggregate in this comparative example, step S3 is as follows: the bamboo aggregate is soaked in an aqueous solution of N-isopropylacrylamide copolymer for 30 minutes.

[0074] Comparative Example 4

[0075] The concrete in this comparative example is basically the same as that in Example 1. The difference is that when preparing the temperature-responsive modified bamboo aggregate in this comparative example, the bamboo aggregate is replaced with an equal weight of limestone crushed stone. The physical and mechanical properties of the limestone crushed stone are consistent with those of the limestone crushed stone in Example 1.

[0076] Comparative Example 5

[0077] The concrete in this comparative example is basically the same as that in Example 1, except that the concrete in this comparative example lacks fucoidan.

[0078] Comparative Example 6

[0079] The concrete in this comparative example is basically the same as that in Example 1, except that the concrete in this comparative example lacks succinic anhydride.

[0080] Comparative Example 7

[0081] The concrete in this comparative example is basically the same as that in Example 1, except that the modified rock wool fiber is replaced with polyvinyl alcohol fiber in this comparative example.

[0082] Test case

[0083] (1) The water absorption rate of aggregates at different water temperatures was tested according to GB / T14685-2022 "Crushed Stone and Pebbles for Construction". The water temperatures were set at 33℃, 20℃, 8℃ and 4℃ respectively. The modified bamboo aggregates in Examples 1-2, bamboo aggregates in Comparative Examples 1-3 and limestone aggregates in Comparative Example 4 were tested in sequence. The test results are shown in Table 1.

[0084] Table 1 Results of aggregate water absorption test

[0085]

[0086] As shown in Table 1, the temperature-responsive modified bamboo aggregates of Examples 1 and 2 had a water absorption rate of 0 at water temperatures of 33℃ and 20℃, respectively, and their aggregate surfaces exhibited excellent hydrophobicity. When the water temperature was 8℃, the water absorption rate changed to around 35%, while at a water temperature of 4℃, the water absorption rates were 74% and 76%, respectively. This indicates that when the temperature-responsive modified bamboo aggregates were around 5-10℃, the copolymer N-isopropylacrylamide on their surface underwent a hydrophilic-hydrophobic transition, and the modified bamboo aggregates began to absorb water at this temperature. In Comparative Example 1, the water absorption rate of ordinary bamboo aggregate remained above 94% at different water temperatures. This directly resulted in it absorbing a large amount of water from the concrete during the early mixing stage, and being unable to absorb water from the capillaries in the hardened concrete at lower temperatures later on. In Comparative Example 2, the water absorption rate of modified bamboo aggregate reached 42% at a water temperature of 20℃. This indicates that replacing dodecyl acrylate with butyl acrylate in the preparation of temperature-responsive modified bamboo aggregate can only adjust the phase transformation temperature to above 20℃, causing the internal temperature of the concrete to drop in the later stage of cement hydration during hardening and forming. The bamboo aggregate had already begun to absorb the water required for hydration, leading to a decrease in concrete strength and density. Furthermore, as the ambient temperature dropped further, the bamboo aggregate essentially lost its ability to absorb water from the concrete capillaries. The results of Comparative Example 3 demonstrated that the absence of crosslinking agents and initiators in the crosslinking-enhanced polymerization treatment of the copolymer N-isopropylacrylamide and bamboo aggregate affected the structural stability and physical properties of the temperature-responsive monomer gel. The gel became relatively loose, resulting in slight water absorption by the aggregate in the early stages of hydration, followed by a decrease in water absorption in the later stages. The limestone aggregate used in Comparative Example 4 exhibited essentially the same water absorption rate at different temperatures. Simultaneously, antifreeze tests were conducted on the bamboo aggregate from Examples 1-2 and the limestone aggregate from Comparative Example 4. After the aggregate became saturated with water, it was further cooled to -18°C and maintained for 36 hours, then thawed at 15°C. After 20 cycles, no significant changes were observed on the surface of the bamboo aggregate from Examples 1-2, while expansion cracks appeared on the surface of the limestone aggregate from Comparative Example 4.

[0087] (2) Performance testing of concrete

[0088] Mechanical properties, impermeability, frost resistance and crack resistance of the concrete in the examples and comparative examples were tested, and the test results are shown in Table 2.

[0089] The mechanical properties of concrete were tested according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Ordinary Concrete"; the impermeability and early crack resistance of concrete were tested according to GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". Before testing, the specimens were subjected to a low-temperature environment: after molding, the specimens were cured at -10℃ for 7 days, followed by standard curing for 28 days. The "permeability height method" was used to determine the average permeability height of the concrete under constant water pressure, representing the concrete's water permeability resistance. The higher the average permeability height, the worse the water permeability resistance. The early crack resistance of concrete was determined using the "crack resistance plate test". The test results were expressed as the calculated total crack area per unit area index; the smaller the value, the better the crack resistance.

[0090] The specific test method for the concrete freeze-thaw resistance test is as follows: Prepare a standard concrete specimen of 150mm×150mm×150mm, cure the specimen at 2±0.5℃ for 7 days, then place the specimen in a rubber specimen box and fill it with water, immersing the specimen in water at 2±0.5℃ for 24 hours. After that, cure it in a low temperature environment of -15℃ for 28 days, test the compressive strength of the specimen, and calculate the ratio of low temperature compressive strength of concrete P = (low temperature curing compressive strength / conventional curing compressive strength) × 100%. The smaller the P value, the greater the strength loss rate and the worse the freeze-thaw resistance of the concrete.

[0091] Table 2 Test Results of Concrete Performance

[0092]

[0093] This invention utilizes succinic anhydride, rock wool fiber, temperature-responsive modified bamboo aggregate, and fucoidan to form a three-tiered defense against freezing and cracking in concrete at low temperatures. It synergistically improves the low-temperature freezing resistance of concrete through four aspects: enhanced cement activity and self-insulation, cooling-responsive water absorption and toughening of modified bamboo aggregate, and increased capillary water setting point. As shown in Table 2, the test results of Examples 1-3 generally demonstrate superior performance, with 28-day compressive strength ranging from 48.0 to 49.3 MPa, water penetration height from 31.2 to 38.4 mm, and total crack area per unit area from 79 to 94 mm². 2 / m 2 All samples had a crack resistance grade of V and a low-temperature compressive strength ratio of 90.3-94.1%. In Example 3, unmodified rock wool fiber was used. Although the indicators were slightly worse than those in Example 1, the overall difference was small.

[0094] Comparative Example 1 uses bamboo aggregate instead of temperature-responsive modified bamboo aggregate. Since the bamboo aggregate is not temperature-responsive modified, it absorbs more water in the early stage of concrete mixing, which affects the normal hydration of concrete. In the later stage, it cannot effectively absorb excess water in the capillary pores of concrete to reduce the stress of capillary water freezing and expansion. Therefore, compared with the performance test results of Example 1, it is significantly inferior in terms of density, crack resistance and frost resistance. The low-temperature compressive strength ratio is only 82.1% and the crack resistance grade is IV.

[0095] In Comparative Example 2, butyl acrylate was used instead of dodecyl acrylate in the preparation of temperature-responsive modified bamboo aggregate. Its low-temperature compressive strength was 5.7 percentage points lower than that of Example 1, and its frost resistance was relatively poor. This is mainly because, compared with the shorter alkyl chain of butyl acrylate, the long alkyl chain of dodecyl acrylate can adjust the critical temperature of the temperature-responsive monomer to a lower level, so that the temperature-responsive aggregate can start to switch between hydrophobicity and water absorption at a lower temperature, and then absorb water from the capillary pores of concrete without affecting the hydration of concrete.

[0096] The antifreeze and crack resistance of Comparative Example 3 were significantly lower than those of Example 1. This indicates that the preparation of bamboo aggregate by simply soaking it in an aqueous solution of N-isopropylacrylamide resulted in a relatively loose and unstable structure of N-isopropylacrylamide, which did not form a good cross-linking structure with the natural fibers on the surface of the bamboo aggregate. As a result, the modified bamboo aggregate failed to fully exert its effective function.

[0097] In Comparative Example 4, the crushed stone was conventional limestone aggregate. Compared to Example 1, its compressive strength under conventional curing was better. However, the water penetration height of the specimens cured at low temperatures increased significantly, and the total crack area per unit area also increased significantly. Furthermore, the low-temperature compressive strength ratio was 76.2%, indicating poor impermeability, crack resistance, and frost resistance of the concrete at low temperatures. This is because concrete using rigid aggregate is prone to rigid expansion at low temperatures, making it susceptible to cracking.

[0098] Compared with Example 1, Comparative Examples 5 to 7 respectively lacked fucoidan, succinic anhydride, and replaced modified rock wool fiber with polyvinyl alcohol fiber. The density, low-temperature freeze-thaw resistance, and crack resistance of the concrete in the comparative examples decreased to varying degrees compared with Example 1. This indicates that the present invention utilizes fucoidan, succinic anhydride, and modified rock wool fiber materials to synergistically improve the low-temperature freeze-thaw resistance and crack resistance of concrete with temperature-responsive modified bamboo aggregate.

[0099] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-temperature frost-resistant and crack-resistant concrete, characterized in that, Its raw materials include the following components: Cementitious materials, sand, crushed stone, temperature-responsive modified bamboo aggregate, water-reducing agent, water, succinic anhydride, fucoidan, rock wool fiber; The preparation method of the temperature-responsive modified bamboo aggregate includes the following steps: S1. N-Isopropylacrylamide and dodecyl acrylate are dissolved in a solvent, initiator one is added, and polymerization reaction is carried out under an inert gas atmosphere. After precipitation, separation and drying, the copolymerized N-isopropylacrylamide monomer is obtained. S2. Dissolve the copolymer N-isopropylacrylamide monomer obtained in step S1 in an aqueous solution of calcium citrate, and stir until homogeneous to obtain an aqueous solution of copolymer N-isopropylacrylamide; S3. Mix bamboo aggregate, aqueous solution of N-isopropylacrylamide copolymer, crosslinking agent and initiator II, and react at 40-50℃ for 4-5 hours to obtain the temperature-responsive modified bamboo aggregate; The cementing materials include cement, fly ash, granulated blast furnace slag, and silica fume; The method for preparing the bamboo aggregate is as follows: mature moso bamboo is crushed into bamboo particles, and after sieving, bamboo aggregate raw materials with a size of 5-15 mm in length, 5-10 mm in width, and 2-3 mm in thickness are obtained. After drying, the bamboo aggregate is obtained. Before use, the rock wool fiber is soaked in a styrene-acrylic copolymer emulsion containing vitrified microspheres, stirred evenly, and then dried.

2. The low-temperature antifreeze and crack-resistant concrete according to claim 1, characterized in that, The molar ratio of N-isopropylacrylamide to dodecyl acrylate is (5~5.5):

1.

3. The low-temperature antifreeze and crack-resistant concrete according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 70-80°C for 3-5 hours.

4. The low-temperature antifreeze and crack-resistant concrete according to claim 1, characterized in that, The mass ratio of the N-isopropylacrylamide monomer, calcium citrate, and water is 1:(0.1~0.2):

5.

5. The low-temperature antifreeze and crack-resistant concrete according to claim 1, characterized in that, The initiator one and initiator two are ammonium persulfate or potassium persulfate. The mass of initiator one is 0.8% to 1.0% of the mass of N-isopropylacrylamide; the mass of initiator two is 1.0% to 1.5% of the mass of the copolymerized N-isopropylacrylamide monomer.

6. The low-temperature antifreeze and crack-resistant concrete according to claim 1, characterized in that, The crosslinking agent is N,N'-methylenebisacrylamide, and the mass of the crosslinking agent is 0.2% to 0.4% of the mass of the copolymerized N-isopropylacrylamide monomer.

7. The low-temperature antifreeze and crack-resistant concrete according to claim 1, characterized in that, By weight, the concrete comprises the following components: 413-486 parts of cementitious material, 710-750 parts of sand, 900-930 parts of crushed stone, 130-160 parts of temperature-responsive modified bamboo aggregate, 5-8 parts of water-reducing agent, 145-155 parts of water, 5-8 parts of succinic anhydride, 1-2 parts of fucoidan, and 2-3 parts of rock wool fiber.

8. A method for preparing low-temperature antifreeze and crack-resistant concrete according to any one of claims 1 to 7, characterized in that, Includes the following steps: The sand, gravel, and cementitious materials are mixed evenly. Then, 2 / 4 water-reducing agent and 2 / 4 water are added and mixed evenly. Next, the temperature-responsive modified bamboo aggregate, rock wool fiber, succinic anhydride, 1 / 4 water-reducing agent, and 1 / 4 water are added and mixed evenly. Finally, fucoidan, 1 / 4 water-reducing agent, and 1 / 4 water are added and mixed evenly to obtain concrete paste.

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