Low-carbon concrete with high crack resistance and water abrasion resistance and preparation method thereof

Abstract

The invention relates to the technical field of low-carbon concrete, in particular to high-crack-resistance water-abrasion-resistant low-carbon concrete and a preparation method thereof. The invention relates to a preparation method of high-crack-resistance and water-abrasion-resistance low-carbon concrete. The preparation method comprises the following steps: preparation of a high-water-absorption polymer, preparation of modified calcium-aluminum hydrotalcite, preparation of reinforced fibers and preparation of the low-carbon concrete. The low-carbon concrete contains the super absorbent polymer, the modified calcium aluminum hydrotalcite and the reinforced fiber, and the super absorbent polymer uses N-vinyl pyrrolidone to retain water and reduce shrinkage; the hydrotalcite fixes chloride ions and fills pores; the three components cooperate with each other, the super absorbent polymer and the hydrotalcite assist in compaction, and the fibers restrain cracking, so that the crack resistance, the permeability resistance and the water abrasion resistance of the concrete are improved from multiple dimensions, and the concrete is suitable for scenes such as water conservancy and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-carbon concrete, and particularly relates to a high-anti-cracking and water-erosion-resistant low-carbon concrete and a preparation method thereof. BACKGROUND

[0002] As a key field of carbon emission, the building industry has become the core direction of the industry development to promote the low-carbon upgrading of concrete materials. The low-carbon concrete usually replaces part of cement by mixing industrial solid waste mineral admixtures such as fly ash, slag powder and silica ash, which not only can reduce the cement consumption and related carbon emission, but also can realize the resource utilization of industrial waste, in line with the development concept of green building materials. However, the large amount of introduction of mineral admixtures will change the hydration process of concrete, leading to the imbalance of the internal free water consumption rate, and easily causing plastic shrinkage cracks and drying shrinkage cracks; at the same time, the lagging nature of the pozzolanic reaction of mineral admixtures will also make the early strength development of concrete slow, and the structure of the interfacial transition zone is relatively loose, which is easy to cause surface erosion, aggregate exposure and other damages under the scouring and grinding action of high-speed water flow with sand and gravel, etc. abrasive, which seriously shortens the service life of concrete structure.

[0003] The anti-cracking performance and water-erosion resistance of concrete are the key indicators to determine the service quality of concrete in special scenes such as water conservancy projects and high-speed water channels. In order to solve the problems of high carbon emission and insufficient anti-cracking performance of traditional concrete, the existing technology usually adds industrial solid waste such as fly ash and slag powder as mineral admixtures to replace part of cement to achieve the low-carbon target and improve the workability and volume stability of concrete. However, the activity of such mineral admixtures is relatively low, and when the replacement amount is large, it is easy to cause the slow development of the early strength of concrete, and the surface anti-erosion ability under water scouring and grinding is decreased. At the same time, simply relying on mineral admixtures modification is difficult to fundamentally solve the anti-cracking problem caused by the low tensile strength and insufficient toughness of concrete. In order to improve the water-erosion resistance of concrete, the existing technology usually adopts the way of increasing the density of concrete or adding steel fibers, polypropylene fibers and other reinforcing phases. Among them, increasing the density usually depends on reducing the water-binder ratio or adding active admixtures such as silica ash, but too low water-binder ratio will cause the workability of concrete to deteriorate, and the construction difficulty increases, and the high activity of silica ash will also aggravate the problem of hydration heat concentration; although steel fibers can significantly improve the impact resistance and wear resistance of concrete, they have the defects of easy corrosion, uneven distribution and high cost, and will increase the resistance of concrete mixing and pumping; the reinforcing effect of polypropylene fibers is limited, and the interface peeling is easy to occur under the action of high-speed water flow scouring and grinding, and the long-term wear resistance is difficult to guarantee.

[0004] In addition, in actual engineering applications, the existing low-carbon concrete often faces the dilemma of being difficult to balance "low carbonization" and "high performance": if the amount of mineral admixture replacement is increased to reduce carbon emissions, the key performance of the concrete, such as crack resistance and water erosion resistance, will be significantly reduced; if the performance is improved by increasing the amount of cement or using high-cost reinforcing materials, it will violate the concept of low-carbon development, and the economy is poor.

[0005] Therefore, it is a technical problem to be solved in the field of concrete materials to develop a concrete material system that can simultaneously realize low cement content, low carbon emission, excellent crack resistance and strong water erosion resistance, and optimize its preparation process. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a low-carbon concrete with high crack resistance and water erosion resistance and a preparation method thereof.

[0007] The present application provides a preparation method of a low-carbon concrete with high crack resistance and water erosion resistance, comprising:

[0008] S1: preparation of a high water-absorbing polymer;

[0009] 2-acrylamide-2-methylpropanesulfonic acid, sodium hydroxide, acrylamide, N-vinylpyrrolidone and N,N'-methylenebisacrylamide are added to deionized water to prepare a mixed monomer solution, Span80 and Tween-80 are added to cyclohexane, then gelatinized starch and potassium persulfate initiator solution are added, and finally the mixed monomer solution is added, reacted to prepare a high water-absorbing polymer;

[0010] S2: preparation of modified calcium-aluminum hydrotalcite;

[0011] The calcium source and aluminum source are added to deionized water to obtain a mixed solution I, sodium hydroxide and urea are added to deionized water, then frozen to minus 1-3℃, then microcrystalline cellulose is added, stirred and mixed to obtain a mixed solution II, the mixed solution I is added to the mixed solution II at a rate of 1-2mL / min, then reacted to prepare the modified calcium-aluminum hydrotalcite;

[0012] S3: preparation of reinforcing fiber;

[0013] First, the TEOS is used for modification treatment of the sisal fiber, and then the water-based polyurethane slurry is used for secondary modification treatment to obtain the reinforcing fiber;

[0014] S4: preparation of low-carbon concrete;

[0015] Prepare the raw materials of concrete by weight parts: cement 300-350 parts, mineral admixture 200-250 parts, fine aggregate 650-750 parts, coarse aggregate 1000-1100 parts, water 130-160 parts, water reducing agent 3-5 parts, superabsorbent polymer 3-5 parts, modified calcium-aluminum hydrotalcite 8-10 parts, and reinforcing fiber 5-8 parts. Mix the raw materials to obtain low-carbon concrete.

[0016] As a preferred aspect, S1: preparation of superabsorbent polymer, specifically comprising the following steps:

[0017] S1.1: 2-3 parts by weight of potassium persulfate is added to 100-120 parts by weight of deionized water, after stirring and mixing, an initiator solution is obtained, 2-3 parts by weight of 2-acrylamide-2-methylpropane sulfonic acid, 0.5-0.8 parts by weight of sodium hydroxide, 2-3 parts by weight of acrylamide, 2-3 parts by weight of N-vinyl pyrrolidone and 0.05-0.06 parts by weight of N,N'-methylene bisacrylamide are added to 100-120 parts by weight of deionized water, stirred and mixed to dissolve, to obtain a mixed monomer solution;

[0018] S1.2: 3-5 parts by weight of starch is added to 50-80 parts by weight of deionized water, then stirred and mixed at 85-90°C for 1-2h to obtain gelatinized starch, 1-2 parts by weight of Span80 and 1-2 parts by weight of Tween-80 are added to 92-95 parts by weight of cyclohexane, stirred at 28-30°C for 20-30min under nitrogen protection, then the gelatinized starch and the initiator solution are added, stirred at 300-320rpm for 1-2min, then the mixed monomer solution is added, and the reaction is carried out at 70-75°C for 2-3h under a nitrogen atmosphere to obtain a reaction product;

[0019] S1.3: pour the reaction product into anhydrous ethanol stirred at 1800-2000rpm, filter to obtain a precipitate, wash the precipitate with anhydrous ethanol for 3-5 times, then dry at 40-50°C for 20-24h to obtain a superabsorbent polymer.

[0020] As a preferred aspect, S2: preparation of modified calcium-aluminum hydrotalcite, specifically comprising the following steps:

[0021] S2.1: 4-6 parts by weight of calcium nitrate and 2-3 parts by weight of aluminum nitrate are added to 30-50 parts by weight of deionized water, stirred and mixed at 300-400rpm for 20-30min to obtain a mixed solution I;

[0022] S2.2: 7-8 parts by weight of sodium hydroxide and 12-15 parts by weight of urea are added to 100-120 parts by weight of deionized water, then frozen to -1 to -3℃, then 0.5-0.8 parts by weight of microcrystalline cellulose is added, and the mixture is stirred at 400-500 rpm for 20-30 min to obtain a mixed solution II;

[0023] S2.3: Under the condition of stirring at 800-1000 rpm, the mixed solution I is added dropwise to the mixed solution II at 1-2 mL / min, so that the pH of the mixed system is 10-11, after the dropwise addition is completed, it is placed for 20-24 h, then added to a high-pressure kettle lined with polytetrafluoroethylene, reacted in a homogeneous reactor at 80-90℃ for 24-26 h, after the reaction is completed, cooled to room temperature, then centrifuged, washed with deionized water for 2-4 times, and finally freeze-dried to obtain the modified calcium-aluminum hydrotalcite.

[0024] As a preferred aspect, S3: preparation of reinforcing fibers, specifically comprising the following steps:

[0025] S3.1: 4-5 parts by weight of TEOS is added to 40-50 parts by weight of anhydrous ethanol, then 20-30 parts by weight of sisal fibers are added, after stirring and mixing, a fiber mixture is obtained, 16-18 parts by weight of anhydrous ethanol and 4-5 parts by weight of deionized water are added to 10-12 parts by weight of ammonia solution with a concentration of 28-30 wt%, and stirred and mixed at 1000-1200 rpm for 1-3 min, then the fiber mixture is added, and stirred and mixed at 350-400 rpm for 2-3 h in a sealed state, then washed with deionized water for 3-5 times, and dried to obtain modified sisal fibers;

[0026] S3.2: The modified sisal fibers are stretched and kept straight, then immersed in an aqueous polyurethane slurry containing 3-5% by mass fraction for 15-20 min, then excess liquid is squeezed out in one direction by using a stick, and then dried at 80-90℃ for 1-2 h to obtain reinforcing fibers.

[0027] As a preferred aspect, S4: preparation of low-carbon concrete, specifically comprising the following steps:

[0028] S4.1: Prepare the concrete raw materials according to the following parts by weight: cement 300-350 parts, mineral admixture 200-250 parts, fine aggregate 650-750 parts, coarse aggregate 1000-1100 parts, water 130-160 parts, water reducing agent 3-5 parts, superabsorbent polymer 3-5 parts, modified calcium-aluminum hydrotalcite 8-10 parts, and reinforcing fibers 5-8 parts;

[0029] S4.2: Add the water-reducing agent to water and stir to obtain a water-reducing agent solution. Put the above-mentioned cement, mineral admixtures, fine aggregate, coarse aggregate, modified calcium aluminum hydrotalcite and superabsorbent polymer into a forced mixer and dry mix at a speed of 90-100 r / min for 60-90 s to obtain a mixture. Then add the water-reducing agent solution and reinforcing fibers and stir at a speed of 90-100 r / min for 10-12 min to obtain low-carbon concrete.

[0030] As a preferred aspect, the water-reducing agent in step S4.1 is a polycarboxylate-based high-performance water-reducing agent.

[0031] As a preferred aspect, the fine aggregate in step S4.1 is one or both of natural river sand and manufactured sand.

[0032] As a preferred aspect, the mineral admixture in step S4.1 is prepared by mixing fly ash, slag powder and silica fume in a mass ratio of 1-2:1-2:1-2.

[0033] As a preferred aspect, the coarse aggregate in step S4.1 is continuously graded crushed stone with a particle size of 5-25 mm.

[0034] The present invention also provides a low-carbon concrete with high crack resistance and water erosion resistance, which is prepared by any of the methods for preparing a low-carbon concrete with high crack resistance and water erosion resistance as described in any one of the claims.

[0035] The present invention has the following advantages:

[0036] 1. This invention incorporates a superabsorbent polymer to prepare low-carbon concrete. This polymer absorbs free water generated during concrete mixing and releases it slowly in the later stages of hydration. This "internal reservoir" effect effectively compensates for water loss caused by hydration and evaporation, reducing plastic shrinkage and drying shrinkage of the concrete. Furthermore, the absorbed water expands and fills the capillary pores inside the concrete, increasing matrix density and enhancing impermeability and water erosion resistance. Additionally, N-vinylpyrrolidone is introduced into the superabsorbent polymer. N-vinylpyrrolidone is a strongly hydrophilic nonionic monomer, and its nonionic groups are insensitive to ion concentration in solution. In concrete, a high-carbon concrete... In alkaline ionic environments, the water absorption capacity of anionic polymers decreases significantly due to the "charge shielding effect." The introduction of N-vinylpyrrolidone can effectively counteract this negative impact, allowing the superabsorbent polymer to maintain a high water absorption rate and water retention capacity even in the harsh chemical environment of concrete pore solutions. This ensures the reliability of the internal curing effect. Furthermore, the carbonyl and amide groups in the N-vinylpyrrolidone molecule can interact with calcium ions or silanol groups on the surface of cement hydration products. This interaction can improve the bonding between the superabsorbent polymer and the cement paste interface, reduce interfacial gaps, and further enhance the crack resistance and water erosion resistance of concrete.

[0037] 2. The modified calcium-aluminum hydrotalcite added in this invention has a unique layered structure. Its layers carry a positive charge. When chloride ions penetrate concrete from the environment, they are captured and fixed between the layers by the hydrotalcite, thus delaying or even preventing chloride ions from reaching the surface of the reinforcing steel, effectively preventing steel corrosion. Furthermore, the dense layered structure of the hydrotalcite can fill the capillary pores inside the concrete, blocking the penetration channels of moisture and harmful ions, enhancing water erosion resistance and chemical corrosion resistance. Moreover, microcrystalline cellulose is introduced during the preparation of the modified calcium-aluminum hydrotalcite for modification; microcrystalline cellulose acts as a structural component... Crystal inhibitors can suppress the lateral growth of calcium aluminum hydrotalcite crystals, causing them to form smaller and thinner nanosheet structures. At the same time, microcrystalline cellulose can form hydrogen bonds with the OH⁻ of calcium aluminum hydrotalcite through hydroxyl groups, encapsulating the surface of calcium aluminum hydrotalcite, enhancing the electrostatic repulsion between modified calcium aluminum hydrotalcite and improving its dispersibility. In addition, smaller and thinner hydrotalcite particles can fill the capillary and gel pores of cement stone, making the microstructure of concrete more compact. This not only improves the compressive strength and toughness but also enhances the concrete's resistance to water erosion.

[0038] 3. This invention incorporates reinforcing fibers into the preparation of low-carbon concrete. These fibers can cross cracks, effectively transfer stress, and dissipate energy, thereby inhibiting crack initiation and preventing micro-cracks from expanding into macro-cracks. This improves the toughness and impact resistance of the concrete. The addition of fibers transforms the concrete from a brittle material into a more resilient composite material, better resisting the repeated action of dynamic water pressure and the cutting of silt particles, thus improving its resistance to water erosion. A dual modification process using TEOS modification and waterborne polyurethane coating overcomes the inherent defects of natural sisal fibers. The silica coating formed after TEOS hydrolysis coats the surface of the sisal fibers, not only improving their resistance to alkali corrosion but also preventing them from being eroded and degraded by the alkaline hydration environment of the concrete. The solution also increases the surface roughness of the fibers; the subsequent waterborne polyurethane coating further enhances the flexibility and tensile toughness of the fibers, reduces fiber breakage during concrete mixing, and ensures that the fibers can effectively play a mechanical reinforcing role in the matrix. The silanol groups introduced by TEOS modification can form chemical bonds with the cement hydration products and the hydroxyl groups of modified calcium aluminum hydrotalcite. The polar groups of waterborne polyurethane can also form hydrogen bonds with the amide groups of superabsorbent polymers and the active sites on the aggregate surface, reducing defects in the interface transition zone between the reinforcing fibers and the concrete matrix, and achieving a tight bond between the "fiber-matrix". This can reduce the cutting and erosion damage to the concrete surface caused by abrasives carried by water flow, enabling low-carbon concrete to have a longer service life in scenarios such as water conservancy projects and high-speed water flow channels.

[0039] 4. In this invention, the superabsorbent polymer, modified calcium aluminum hydrotalcite, and reinforcing fibers can form a synergistically reinforcing composite system within the concrete. The internal curing effect of the superabsorbent polymer promotes the full hydration of cement, and together with the pore-filling effect of the modified calcium aluminum hydrotalcite, it contributes to the micro-densification of the matrix. The uniformly dispersed reinforcing fibers constrain the shrinkage and cracking of the matrix on a macroscopic scale. Meanwhile, the modified calcium aluminum hydrotalcite, while increasing density, provides additional protection for the reinforcing steel through its chloride ion curing function. These three components each play their respective roles while complementing each other, jointly improving the crack resistance, impermeability, and water erosion resistance of low-carbon concrete from multiple dimensions, including physical filling, chemical curing, and mechanical reinforcement. Attached Figure Description

[0040] Figure 1 This invention relates to a method for preparing low-carbon concrete with high crack resistance and water erosion resistance, as used in an embodiment of the invention. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0042] Example 1: A method for preparing low-carbon concrete with high crack resistance and water erosion resistance, referring to... Figure 1 ,include:

[0043] S1: Preparation of superabsorbent polymer;

[0044] S1.1: Add 2 parts by weight of potassium persulfate to 100 parts by weight of deionized water, stir and mix to obtain an initiator solution. Add 2 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 0.5 parts by weight of sodium hydroxide, 2 parts by weight of acrylamide, 2 parts by weight of N-vinylpyrrolidone and 0.05 parts by weight of N,N'-methylenebisacrylamide to 100 parts by weight of deionized water, stir and mix to dissolve to obtain a mixed monomer solution.

[0045] S1.2: Add 3 parts by weight of starch to 50 parts by weight of deionized water, and then stir and mix at 85°C for 1 hour to obtain gelatinized starch. Add 1 part by weight of Span80 and 1 part by weight of Tween-80 to 92 parts by weight of cyclohexane, and stir at 28°C for 20 minutes under nitrogen protection. Then add gelatinized starch and initiator solution, stir at 300 rpm for 1 minute, and then add mixed monomer solution. React at 70°C for 2 hours under nitrogen atmosphere to obtain reactant.

[0046] S1.3: The reactants were poured into anhydrous ethanol stirred at 1800 rpm, filtered to obtain a precipitate, washed three times with anhydrous ethanol, and then dried at 40°C for 20 h to obtain a superabsorbent polymer.

[0047] S2: Preparation of modified calcium aluminum hydrotalcite;

[0048] S2.1: Add 4 parts by weight of calcium nitrate and 2 parts by weight of aluminum nitrate to 30 parts by weight of deionized water, and stir at 300 rpm for 20 min to obtain mixture I;

[0049] S2.2: Add 7 parts by weight of sodium hydroxide and 12 parts by weight of urea to 100 parts by weight of deionized water, then freeze to -1°C, then add 0.5 parts by weight of microcrystalline cellulose, and stir at 400 rpm for 20 min to obtain mixture II.

[0050] S2.3: Under stirring at 800 rpm, mixture I was added dropwise to mixture II at 1 mL / min to make the pH of the mixture 10. After the addition was complete, the mixture was allowed to stand for 20 h, and then added to a high-pressure reactor lined with polytetrafluoroethylene. The mixture was reacted at 80 °C for 24 h in a homogeneous reactor. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed twice with deionized water, and finally freeze-dried to obtain modified calcium aluminum hydrotalcite.

[0051] S3: Preparation of reinforcing fibers;

[0052] S3.1: Add 4 parts by weight of TEOS to 40 parts by weight of anhydrous ethanol, then add 20 parts by weight of sisal fiber, stir and mix to obtain a fiber mixture. Add 16 parts by weight of anhydrous ethanol and 4 parts by weight of deionized water to 10 parts by weight of ammonia solution with a concentration of 28wt%, stir and mix at 1000 rpm for 1 min, then add the fiber mixture, stir and mix under a closed system at 350 rpm for 2 h, then wash with deionized water 3 times, dry to obtain modified sisal fiber.

[0053] S3.2: Tighten the modified sisal fiber and keep it taut. Then immerse it in a water-based polyurethane slurry containing 3% by mass for 15 minutes. After that, use a stick to squeeze out the excess liquid in one direction. Then dry it at 80°C for 1 hour to obtain the reinforced fiber.

[0054] S4: Preparation of low-carbon concrete;

[0055] S4.1: Prepare concrete raw materials according to the following parts by weight: 300 parts cement, 200 parts mineral admixtures, 650 parts fine aggregate, 1000 parts coarse aggregate, 130 parts water, 3 parts water-reducing agent, 3 parts superabsorbent polymer, 8 parts modified calcium aluminum hydrotalcite and 5 parts reinforcing fiber.

[0056] Among them, the mineral admixture is made by mixing fly ash, slag powder and silica fume in a mass ratio of 1:1:1, and the fine aggregate is made by mixing natural river sand and manufactured sand in a mass ratio of 1:1.

[0057] S4.2: Add the water-reducing agent to water and stir to obtain a water-reducing agent solution. Put the above-mentioned cement, mineral admixtures, fine aggregate, coarse aggregate, modified calcium aluminum hydrotalcite and superabsorbent polymer into a forced mixer and dry mix at 90 r / min for 60 s to obtain a mixture. Then add the water-reducing agent solution and reinforcing fibers and stir at 90 r / min for 10 s to obtain low-carbon concrete.

[0058] Example 2: A method for preparing low-carbon concrete with high crack resistance and water erosion resistance, see [link to example]. Figure 1 ,include:

[0059] S1: Preparation of superabsorbent polymer;

[0060] S1.1: Add 3 parts by weight of potassium persulfate to 120 parts by weight of deionized water, stir and mix to obtain an initiator solution. Add 3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 0.8 parts by weight of sodium hydroxide, 3 parts by weight of acrylamide, 3 parts by weight of N-vinylpyrrolidone and 0.06 parts by weight of N,N'-methylenebisacrylamide to 120 parts by weight of deionized water, stir and mix to dissolve to obtain a mixed monomer solution.

[0061] S1.2: Add 5 parts by weight of starch to 80 parts by weight of deionized water, and then stir and mix at 90°C for 2 hours to obtain gelatinized starch. Add 2 parts by weight of Span80 and 2 parts by weight of Tween-80 to 95 parts by weight of cyclohexane, and stir at 30°C for 30 minutes under nitrogen protection. Then add gelatinized starch and initiator solution, stir at 320 rpm for 2 minutes, and then add mixed monomer solution. React at 75°C for 3 hours under nitrogen atmosphere to obtain reactant.

[0062] S1.3: The reactants were poured into anhydrous ethanol stirred at 2000 rpm, filtered to obtain a precipitate, washed 5 times with anhydrous ethanol, and then dried at 50°C for 24 h to obtain a superabsorbent polymer.

[0063] S2: Preparation of modified calcium aluminum hydrotalcite;

[0064] S2.1: Add 6 parts by weight of calcium nitrate and 3 parts by weight of aluminum nitrate to 50 parts by weight of deionized water, and stir at 400 rpm for 30 min to obtain mixture I;

[0065] S2.2: Add 8 parts by weight of sodium hydroxide and 15 parts by weight of urea to 120 parts by weight of deionized water, then freeze to -3°C, then add 0.8 parts by weight of microcrystalline cellulose, and stir at 500 rpm for 30 min to obtain mixture II;

[0066] S2.3: Under stirring at 1000 rpm, mixture I was added dropwise to mixture II at 2 mL / min to make the pH of the mixture 11. After the addition was complete, the mixture was allowed to stand for 24 h, and then added to a high-pressure reactor lined with polytetrafluoroethylene. The mixture was reacted at 90 °C for 26 h in a homogeneous reactor. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed 4 times with deionized water, and finally freeze-dried to obtain modified calcium aluminum hydrotalcite.

[0067] S3: Preparation of reinforcing fibers;

[0068] S3.1: Add 5 parts by weight of TEOS to 50 parts by weight of anhydrous ethanol, then add 30 parts by weight of sisal fiber, stir and mix to obtain a fiber mixture. Add 18 parts by weight of anhydrous ethanol and 5 parts by weight of deionized water to 12 parts by weight of a 30 wt% ammonia solution, stir and mix at 1200 rpm for 3 min, then add the fiber mixture, stir and mix under closed conditions at 400 rpm for 3 h, then wash with deionized water 5 times, dry to obtain modified sisal fiber.

[0069] S3.2: Tighten the modified sisal fiber and keep it taut. Then immerse it in a water-based polyurethane slurry containing 5% by mass for 20 minutes. After that, use a stick to squeeze out the excess liquid in one direction. Then dry it at 90°C for 2 hours to obtain the reinforced fiber.

[0070] S4: Preparation of low-carbon concrete;

[0071] S4.1: Prepare concrete raw materials according to the following parts by weight: 350 parts cement, 250 parts mineral admixtures, 750 parts fine aggregate, 1100 parts coarse aggregate, 160 parts water, 5 parts water-reducing agent, 5 parts superabsorbent polymer, 10 parts modified calcium aluminum hydrotalcite and 8 parts reinforcing fiber.

[0072] Among them, the mineral admixture is prepared by mixing fly ash, slag powder and silica fume in a mass ratio of 2:2:1, and the fine aggregate is prepared by mixing natural river sand and manufactured sand in a mass ratio of 1:2.

[0073] S4.2: Add the water-reducing agent to water and stir to obtain a water-reducing agent solution. Put the above-mentioned cement, mineral admixtures, fine aggregate, coarse aggregate, modified calcium aluminum hydrotalcite and superabsorbent polymer into a forced mixer and dry mix at 100 r / min for 90 s to obtain a mixture. Then add the water-reducing agent solution and reinforcing fibers and stir at 100 r / min for 12 min to obtain low-carbon concrete.

[0074] Example 3: A method for preparing low-carbon concrete with high crack resistance and water erosion resistance, see [link to example]. Figure 1 ,include:

[0075] S1: Preparation of superabsorbent polymer;

[0076] S1.1: Add 2.5 parts by weight of potassium persulfate to 110 parts by weight of deionized water, stir and mix to obtain an initiator solution. Add 2.5 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 0.65 parts by weight of sodium hydroxide, 2.5 parts by weight of acrylamide, 2.5 parts by weight of N-vinylpyrrolidone and 0.055 parts by weight of N,N'-methylenebisacrylamide to 110 parts by weight of deionized water, stir and mix to dissolve, and obtain a mixed monomer solution.

[0077] S1.2: Add 4 parts by weight of starch to 65 parts by weight of deionized water, and then stir and mix at 86.5℃ for 1.5h to obtain gelatinized starch. Add 1.5 parts by weight of Span80 and 1.5 parts by weight of Tween-80 to 93.5 parts by weight of cyclohexane, and stir at 29℃ for 25min under nitrogen protection. Then add gelatinized starch and initiator solution, stir at 310rpm for 1.5min, and then add mixed monomer solution. React at 72.5℃ for 2.5h under nitrogen atmosphere to obtain reactant.

[0078] S1.3: The reactants were poured into anhydrous ethanol stirred at 1900 rpm, filtered to obtain a precipitate, washed 4 times with anhydrous ethanol, and then dried at 45°C for 22 h to obtain a superabsorbent polymer.

[0079] S2: Preparation of modified calcium aluminum hydrotalcite;

[0080] S2.1: Add 5 parts by weight of calcium nitrate and 2.5 parts by weight of aluminum nitrate to 40 parts by weight of deionized water, and stir at 350 rpm for 25 min to obtain mixture I;

[0081] S2.2: Add 7.5 parts by weight of sodium hydroxide and 13.5 parts by weight of urea to 110 parts by weight of deionized water, then freeze to -2°C, then add 0.65 parts by weight of microcrystalline cellulose, and stir at 450 rpm for 25 min to obtain mixture II.

[0082] S2.3: Under stirring at 900 rpm, mixture I was added dropwise to mixture II at 1.5 mL / min to make the pH of the mixture 10.5. After the addition was complete, the mixture was allowed to stand for 22 h, and then added to a high-pressure reactor lined with polytetrafluoroethylene. The mixture was reacted at 85 °C for 25 h in a homogeneous reactor. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and finally freeze-dried to obtain modified calcium aluminum hydrotalcite.

[0083] S3: Preparation of reinforcing fibers;

[0084] S3.1: Add 4.5 parts by weight of TEOS to 45 parts by weight of anhydrous ethanol, then add 25 parts by weight of sisal fiber, stir and mix to obtain a fiber mixture. Add 17 parts by weight of anhydrous ethanol and 4.5 parts by weight of deionized water to 11 parts by weight of ammonia solution with a concentration of 29 wt%, stir and mix at 1100 rpm for 2 min, then add the fiber mixture, stir and mix under closed conditions at 375 rpm for 2-3 h, then wash with deionized water 4 times, dry to obtain modified sisal fiber;

[0085] S3.2: Tighten the modified sisal fiber and keep it taut. Then immerse it in an aqueous polyurethane slurry containing 4% by mass for 17.5 minutes. After that, use a stick to squeeze out the excess liquid in one direction. Then dry it at 85°C for 1.5 hours to obtain the reinforced fiber.

[0086] S4: Preparation of low-carbon concrete;

[0087] S4.1: Prepare concrete raw materials according to the following parts by weight: 325 parts cement, 225 parts mineral admixtures, 700 parts fine aggregate, 1050 parts coarse aggregate, 145 parts water, 4 parts water-reducing agent, 4 parts superabsorbent polymer, 9 parts modified calcium aluminum hydrotalcite and 6.5 parts reinforcing fiber.

[0088] Among them, the mineral admixture is prepared by mixing fly ash, slag powder and silica fume in a mass ratio of 1:1:2, and the fine aggregate is prepared by mixing natural river sand and manufactured sand in a mass ratio of 2:1.

[0089] S4.2: Add the water-reducing agent to water and stir to obtain a water-reducing agent solution. Put the above-mentioned cement, mineral admixtures, fine aggregate, coarse aggregate, modified calcium aluminum hydrotalcite and superabsorbent polymer into a forced mixer and dry mix at a speed of 95 r / min for 75 s to obtain a mixture. Then add the water-reducing agent solution and reinforcing fibers and stir at a speed of 95 r / min for 11 min to obtain low-carbon concrete.

[0090] Comparative Example 1 differs from Example 1 in that the superabsorbent polymer, modified calcium aluminum hydrotalcite and reinforcing fiber in steps S1-S3 and S4.1 are removed, while the remaining steps remain unchanged to prepare low-carbon concrete. This is referred to as Comparative Example 1.

[0091] Comparative Example 2 differs from Example 1 in that step S1 is removed, and the superabsorbent polymer in step S4.1 is replaced with an equal amount of polyacrylic acid, while the remaining steps remain unchanged to prepare low-carbon concrete. This is referred to as Comparative Example 2.

[0092] Comparative Example 3 differs from Example 1 in that N-vinylpyrrolidone in step S1.1 is removed, while the remaining steps remain unchanged in preparing low-carbon concrete. This example is referred to as Comparative Example 3.

[0093] Comparative Example 4 differs from Example 1 in that it involves removing microcrystalline cellulose in step S2.2 while keeping the other steps unchanged in preparing low-carbon concrete.

[0094] Comparative Example 5 differs from Example 1 in that step S3 is removed, and the reinforcing fiber in step S4.1 is replaced with an equal amount of sisal fiber, while the remaining steps remain unchanged in preparing low-carbon concrete. This is referred to as Comparative Example 5.

[0095] The low-carbon concrete prepared in Examples 1-3 and Comparative Examples 1-5 was poured and cured for 28 days according to standard concrete specimens to obtain each concrete specimen.

[0096] Compressive strength test: The compressive strength of concrete specimens was tested using a pressure testing machine in accordance with the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T50081-2002).

[0097] Crack resistance test: The square and round crack resistance test was adopted. The low carbon concrete prepared in Examples 1-3 and Comparative Examples 1-5 were poured according to the standard concrete specimens and cured for 3 days. Then, they were transferred to the oven and forced to crack at 120°C for 28 days. The total area of ​​cracks in the concrete specimens was measured.

[0098] Water abrasion resistance test: Refer to the "Test Procedure for Hydraulic Concrete" (DL / T5150-2001), abrasion tester is used to abrade the concrete specimens for 72 hours at a water flow rate of 12 m / s, and the mass loss rate of the concrete specimens is calculated.

[0099] The performance of concrete specimens prepared in Examples 1-3 and Comparative Examples 1-5 was measured three times, and the average value was taken. The results are shown in Table 1.

[0100] Table 1. Performance test results of Examples 1-3 and Comparative Examples 1-5

[0101]

[0102] As can be seen from the data in Table 1, the data in Comparative Example 1 is worse than that in the Example 1, indicating that the addition of superabsorbent polymer, modified calcium aluminum hydrotalcite, and reinforcing fibers in this invention collectively improves the crack resistance and water abrasion resistance of low-carbon concrete. The data from Comparative Examples 2-3 show that the novel superabsorbent polymer prepared in this invention exhibits better "internal curing" effect, crack resistance, and water abrasion resistance in concrete under high-alkali conditions than traditional polyacrylic acid, and the addition of N-vinylpyrrolidone further enhances crack resistance and abrasion resistance. The data from Comparative Example 4 shows that the hydrotalcite without microcrystalline cellulose modification has poor crack resistance and abrasion resistance because its dispersibility is poor, resulting in unsatisfactory reinforcement, crack resistance, and abrasion resistance. This indicates that the introduction of microcrystalline cellulose effectively inhibits crystal growth and improves dispersion, thus effectively improving crack resistance and water abrasion resistance. The data from Comparative Example 5 shows that the modified sisal fiber can significantly improve the crack resistance, water abrasion resistance, and compressive strength of concrete.

[0103] The concrete specimens prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to drying shrinkage tests in accordance with GB / T50082-2009. The tests were performed three times, and the average value was taken. The test results are shown in Table 2.

[0104] Table 2. Results of drying shrinkage performance tests for Examples 1-3 and Comparative Examples 1-3

[0105]

[0106] As can be seen from the data in Table 2, the drying shrinkage values ​​of Examples 1-3 are significantly lower than those of Comparative Example 1, indicating that the synergistic system of superabsorbent polymer, modified calcium aluminum hydrotalcite and reinforcing fiber introduced in this invention has an extremely significant effect on inhibiting concrete drying shrinkage and preventing cracking. As can be seen from the data in Comparative Example 2, the superabsorbent polymer prepared in this invention has a better "internal curing" effect than the traditional ordinary polyacrylic acid superabsorbent polymer. As can be seen from the data in Comparative Example 3, the introduction of N-vinylpyrrolidone can further improve the "internal curing" effect and reduce concrete drying shrinkage.

[0107] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A method for preparing low-carbon concrete with high crack resistance and water erosion resistance, characterized in that, include: S1: Preparation of superabsorbent polymer; 2-Acrylamide-2-methylpropanesulfonic acid, sodium hydroxide, acrylamide, N-vinylpyrrolidone, and N,N'-methylenebisacrylamide were added to deionized water to prepare a mixed monomer solution. Span80 and Tween-80 were added to cyclohexane, followed by the addition of gelatinized starch and potassium persulfate initiator solution. Finally, the mixed monomer solution was added, and the reaction was carried out to prepare a superabsorbent polymer. S2: Preparation of modified calcium aluminum hydrotalcite; Calcium and aluminum sources were added to deionized water to obtain mixture I. Sodium hydroxide and urea were added to deionized water and then frozen to -1 to -3°C. Microcrystalline cellulose was then added and stirred to obtain mixture II. Mixture I was added dropwise to mixture II at 1-2 mL / min and then reacted to prepare modified calcium aluminum hydrotalcite. S3: Preparation of reinforcing fibers; First, TEOS was used to modify the sisal fiber, and then water-based polyurethane slurry was used for secondary modification to obtain reinforced fiber. S4: Preparation of low-carbon concrete; Prepare concrete raw materials by weight: 300-350 parts cement, 200-250 parts mineral admixtures, 650-750 parts fine aggregate, 1000-1100 parts coarse aggregate, 130-160 parts water, 3-5 parts water-reducing agent, 3-5 parts superabsorbent polymer, 8-10 parts modified calcium aluminum hydrotalcite, and 5-8 parts reinforcing fiber. Mix all raw materials to obtain low-carbon concrete.

2. The method for preparing a low-carbon concrete with high crack resistance and water erosion resistance according to claim 1, characterized in that, S1: The preparation of the superabsorbent polymer includes the following steps: S1.1: Add 2-3 parts by weight of potassium persulfate to 100-120 parts by weight of deionized water, stir and mix to obtain an initiator solution. Add 2-3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 0.5-0.8 parts by weight of sodium hydroxide, 2-3 parts by weight of acrylamide, 2-3 parts by weight of N-vinylpyrrolidone and 0.05-0.06 parts by weight of N,N'-methylenebisacrylamide to 100-120 parts by weight of deionized water, stir and mix to dissolve to obtain a mixed monomer solution. S1.2: Add 3-5 parts by weight of starch to 50-80 parts by weight of deionized water, and then stir and mix at 85-90℃ for 1-2 hours to obtain gelatinized starch. Add 1-2 parts by weight of Span80 and 1-2 parts by weight of Tween-80 to 92-95 parts by weight of cyclohexane, and stir at 28-30℃ for 20-30 minutes under nitrogen protection. Then add gelatinized starch and initiator solution, stir at 300-320 rpm for 1-2 minutes, and then add mixed monomer solution. React at 70-75℃ under nitrogen atmosphere for 2-3 hours to obtain reactant. S1.3: Pour the reactants into anhydrous ethanol stirred at 1800-2000 rpm, filter to obtain a precipitate, wash the precipitate 3-5 times with anhydrous ethanol, and then dry it at 40-50℃ for 20-24 h to obtain a superabsorbent polymer.

3. The method for preparing a low-carbon concrete with high crack resistance and water erosion resistance according to claim 2, characterized in that, S2: The preparation of modified calcium aluminum hydrotalcite includes the following steps: S2.1: Add 4-6 parts by weight of calcium nitrate and 2-3 parts by weight of aluminum nitrate to 30-50 parts by weight of deionized water, and stir and mix at 300-400 rpm for 20-30 min to obtain mixture I; S2.2: Add 7-8 parts by weight of sodium hydroxide and 12-15 parts by weight of urea to 100-120 parts by weight of deionized water, then freeze to -1 to -3°C, then add 0.5-0.8 parts by weight of microcrystalline cellulose, and stir and mix at 400-500 rpm for 20-30 min to obtain mixture II. S2.3: Under stirring at 800-1000 rpm, add mixture I dropwise to mixture II at 1-2 mL / min to make the pH of the mixture 10-11. After the addition is complete, let it stand for 20-24 h, then add it to a high-pressure reactor lined with polytetrafluoroethylene and react in a homogeneous reactor at 80-90℃ for 24-26 h. After the reaction is complete, cool to room temperature, then centrifuge, wash with deionized water 2-4 times, and finally freeze dry to obtain modified calcium aluminum hydrotalcite.

4. The method for preparing a low-carbon concrete with high crack resistance and water erosion resistance according to claim 3, characterized in that, S3: Preparation of reinforcing fibers, specifically including the following steps: S3.1: Add 4-5 parts by weight of TEOS to 40-50 parts by weight of anhydrous ethanol, then add 20-30 parts by weight of sisal fiber, stir and mix to obtain a fiber mixture. Add 16-18 parts by weight of anhydrous ethanol and 4-5 parts by weight of deionized water to 10-12 parts by weight of ammonia solution with a concentration of 28-30wt%, stir and mix at 1000-1200 rpm for 1-3 min, then add the fiber mixture, stir and mix under closed conditions at 350-400 rpm for 2-3 h, then wash with deionized water 3-5 times, dry to obtain modified sisal fiber; S3.2: Tighten the modified sisal fibers and keep them taut. Then immerse them in an aqueous polyurethane slurry containing 3-5% by mass for 15-20 minutes. After that, use a stick to squeeze out the excess liquid in one direction. Then dry them at 80-90℃ for 1-2 hours to obtain the reinforced fibers.

5. The method for preparing a low-carbon concrete with high crack resistance and water erosion resistance according to claim 4, characterized in that, S4: The preparation of low-carbon concrete includes the following steps: S4.1: Prepare concrete raw materials according to the following weight parts: 300-350 parts cement, 200-250 parts mineral admixtures, 650-750 parts fine aggregate, 1000-1100 parts coarse aggregate, 130-160 parts water, 3-5 parts water-reducing agent, 3-5 parts superabsorbent polymer, 8-10 parts modified calcium aluminum hydrotalcite, and 5-8 parts reinforcing fiber; S4.2: Add the water-reducing agent to water and stir to obtain a water-reducing agent solution. Put the above-mentioned cement, mineral admixtures, fine aggregate, coarse aggregate, modified calcium aluminum hydrotalcite and superabsorbent polymer into a forced mixer and dry mix at a speed of 90-100 r / min for 60-90 s to obtain a mixture. Then add the water-reducing agent solution and reinforcing fibers and stir at a speed of 90-100 r / min for 10-12 min to obtain low-carbon concrete.

6. The method for preparing low-carbon concrete with high crack resistance and water erosion resistance according to claim 5, characterized in that, The water-reducing agent in step S4.1 is a polycarboxylate-based high-performance water-reducing agent.

7. The method for preparing a low-carbon concrete with high crack resistance and water erosion resistance according to claim 5, characterized in that, The fine aggregate in step S4.1 is one or both of natural river sand and manufactured sand.

8. The method for preparing a low-carbon concrete with high crack resistance and water erosion resistance according to claim 5, characterized in that, The mineral admixture in step S4.1 is prepared by mixing fly ash, slag powder and silica fume in a mass ratio of 1-2:1-2:1-2.

9. The method for preparing a low-carbon concrete with high crack resistance and water erosion resistance according to claim 5, characterized in that, The coarse aggregate in step S4.1 is continuously graded crushed stone with a particle size of 5-25mm.

10. A low-carbon concrete with high crack resistance and resistance to water erosion, characterized in that, It is prepared by the method for preparing a low-carbon concrete with high crack resistance and water erosion resistance as described in any one of claims 1-9.

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