Green material for cofferdam and preparation method thereof

Abstract

This invention relates to the field of backfill technology, specifically to a green material for backfilling cofferdam boreholes and its preparation method. The green material for backfilling cofferdam boreholes comprises the following components by weight: 21-33 parts cement, 3.5-4.5 parts bentonite, 60-70 parts clay, 3-5 parts modified sawdust, 60-66 parts deionized water, and 2-6 parts modified fiber. The green material for backfilling cofferdam boreholes prepared by this invention has good hydration ability and strong compressive strength. Furthermore, through the combination of modified sawdust and modified fiber, a mechanical interlocking effect is formed between them, effectively improving the cohesiveness of the prepared backfill material.

Description

Technical Field

[0001] This invention relates to the field of backfill technology, specifically to a green material for backfilling dike boreholes and its preparation method. Background Technology

[0002] In recent years, with economic development, bridge projects have become increasingly common in infrastructure construction. Cofferdam construction techniques are frequently used in bridge construction, often employing underwater pier abutments. Cofferdams serve as water-sealing and retaining structures, and are commonly used in bridge construction for pile foundations and open-cut foundations. They are generally suitable for foundation projects with thick overburden layers such as sandy soil, gravelly soil, semi-dry clay, and soft, completely weathered rock. However, driving sheet piles presents challenges in harder rock formations and complex geological conditions. In such cases, it is necessary to first use a rotary drilling rig to create pilot holes in the cofferdam, followed by backfilling with a mixture to facilitate the subsequent driving of sheet piles, pipe piles, or concrete piles.

[0003] Currently used backfill materials are mostly cement-based composite materials or mixtures containing mineral admixtures. Although these materials have certain strength and adhesion, there are still many technical defects and room for improvement in practical engineering applications, mainly in the following aspects: ① Insufficient dispersibility: To enhance the hydration reaction of backfill materials, existing formulations often add active reinforcing materials such as nano-silica and nano-alumina. However, due to their large specific surface area and strong agglomeration, nanomaterials are often difficult to disperse uniformly in the matrix, resulting in reduced hydration efficiency, low material utilization, and affecting the overall performance of the backfill material. ② Poor material synergy: In existing backfill systems, the various components are mostly physically mixed, lacking chemical reactions or synergistic coupling effects, resulting in weak interfacial bonding, loose overall material structure, poor cohesion, and difficulty in forming an efficient load-bearing body or effective force transmission layer. ③ Insufficient environmental performance: Some backfill material formulations use industrial by-products (such as fly ash, slag, etc.) that have not undergone green modification treatment, posing environmental risks such as the release of heavy metal ions, which is not conducive to the promotion of green foundation engineering material systems.

[0004] Therefore, there is an urgent need to develop a new type of green material for backfilling cofferdam boreholes that has good dispersibility, high cohesion, strong material synergy, and is environmentally friendly, in order to meet the needs of pile foundation construction under complex geological conditions, improve the driving efficiency and engineering stability of sheet piles, steel pipe piles, or concrete piles, and provide reliable material support for the construction of infrastructure such as bridges. Summary of the Invention

[0005] The purpose of this invention is to provide a green material for backfilling cofferdam boreholes and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A green material for backfilling cofferdam boreholes, comprising the following components by weight: 21-33 parts cement, 3.5-4.5 parts bentonite, 60-70 parts clay, 3-5 parts modified sawdust, 60-66 parts deionized water, and 2-6 parts modified fiber; The modified sawdust is prepared by the following steps: S101. Crush the sawdust using a pulverizer and pass it through a 100-mesh sieve. Soak the crushed sawdust in an alkaline solution for 1-3 hours, centrifuge and filter, and freeze-dry the product at -40 to -80°C for 12-24 hours. S102. The sawdust treated in step S101 is soaked in a mixed solution of hydrogen peroxide and sodium hypochlorite for 1-5 hours. The filtered product is then continuously treated with ozone at a concentration of 40 ppm for 0.5-1 hours. During the ozone treatment, the product is heated at a temperature of 80°C. S103. Add the sawdust treated in step S102 to deionized water, then add modified mesoporous silica, continuously ultrasonically disperse for 1-2 hours, and then rotary evaporate at 70°C to obtain modified sawdust. The modified fiber is a short-cut carbon fiber coated with polydopamine; The method for preparing the modified fiber includes the following steps: S201. Disperse short-cut carbon fibers in acetone and heat under reflux at 80°C for 18 hours. Then filter the mixture, wash the product with sufficient deionized water and dry it at 50°C. S202. The short-cut carbon fibers treated in step S201 are impregnated in a Tris-HCl buffer solution containing dopamine hydrochloride at pH 8.5 and shaken on a shaker for 24 hours at a shaking speed of 300 rpm / min. After that, the mixture is filtered, washed with sufficient deionized water, and dried at 80°C.

[0007] Furthermore, the method for preparing modified mesoporous silica in step S103 includes the following steps; S301. Place the mesoporous silica in a muffle furnace and calcine it at 350~500℃ for 5 hours; S302. Disperse the mesoporous silica calcined in step S301 into a calcium chloride solution and soak it for 2-3 hours. Then filter it and dry the filtered product at 50°C. S303. The mesoporous silica treated in step S302 is added to a deionized aqueous solution of oxidized starch, and then spray-dried to obtain modified mesoporous silica.

[0008] Furthermore, the alkaline solution in step S101 is a sodium hydroxide solution with a concentration of 1 mol / L; the alkaline solution also contains 3-aminopropyltriethoxysilane with a concentration of 1 wt%.

[0009] Furthermore, in step S102, the concentration of hydrogen peroxide is 10 wt% and the concentration of sodium hypochlorite is 0.15 mol / L; the mass ratio between the sawdust treated in step S101 and the mixed solution of hydrogen peroxide and sodium hypochlorite is 1:(20~30).

[0010] Furthermore, in step S103, the mass ratio between the modified mesoporous silica, deionized water, and sawdust treated in step S102 is 1:(30~45):(5~10).

[0011] Furthermore, in step S301, the particle size of the mesoporous silica is 200~500nm, and in step S302, the concentration of the calcium chloride solution is 2mol / L.

[0012] Furthermore, in step S303, the mass ratio between oxidized starch and deionized water is 1:(10-20), and the mass ratio between oxidized starch and mesoporous silica in step S301 is 1:(1-2).

[0013] Furthermore, in step S202, the mass ratio between the short-cut carbon fibers, dopamine hydrochloride, and Tris-HCl buffer is 1:(0.2~1):(50~70).

[0014] A method for preparing green material for backfilling dike inlet holes, the method comprising the following steps: S1. Disperse the modified fiber and modified sawdust into deionized water according to the mass parts, and stir continuously for 1 hour to obtain a mixture; S2. Add cement, bentonite and clay to the mixture obtained in step S1 according to the mass ratio, and continue mixing for 0.5 hours to obtain the green material for backfilling the cofferdam inlet.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, modified sawdust is added to improve the performance of the backfill material. The sawdust is first treated with alkali to form a large number of pores on its surface, and then undergoes two-step oxidation to form a large number of active sites on its surface, which combine with mesoporous silica. Its pozzolanic effect is beneficial to the hydration process and improves the strength of the backfill material. Since the mesoporous silica is nanoscale, it enters the backfill material through the sawdust, which facilitates the dispersion of the mesoporous silica. The mesoporous silica is loaded with calcium ions to supplement the reaction system and improve the hydration capacity. In addition, by drying and spraying oxidized starch together with mesoporous silica, the oxidized starch improves the bonding ability between mesoporous silica and sawdust, and at the same time, it delays the exposure of mesoporous silica in the alkaline environment, allowing it to continue to play its role. 2. This invention incorporates chopped carbon fibers, the surface of which is coated with polydopamine. The amino groups of polydopamine readily bind to the active surface of sawdust, enhancing the cohesiveness of the backfill material. During the formation of the polydopamine-coated material, vibration in a shaker promotes the formation of polydopamine particles on the polydopamine surface, effectively increasing the surface roughness of the polydopamine layer and enhancing its mechanical interlocking with sawdust and other materials, further improving the overall cohesiveness of the material. The sawdust used in this invention is a renewable resource, and bentonite and clay are both natural minerals, environmentally friendly, and excellent green materials suitable for widespread application. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the preparation of green materials for backfilling the cofferdam borehole in this invention; Figure 2 This is a process flow diagram for preparing modified sawdust in this invention; Figure 3 This is a process flow diagram for preparing modified fibers in this invention; Figure 4 This is a process flow diagram for preparing modified mesoporous silica in this invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0018] Please see Figures 1 to 4 The present invention provides: Example 1 A method for preparing green material for backfilling dike inlet holes, the method comprising the following steps: S1. Disperse 50g of modified fiber and 40g of modified sawdust into 640g of deionized water and stir continuously for 1 hour to obtain a mixture; S2. Add 250g of cement, 40g of bentonite and 650g of clay to the mixture obtained in step S1, and continue mixing for 0.5h to obtain the green material for backfilling the cofferdam inlet.

[0019] The modified sawdust described above was prepared by the following steps: S101. Crush 70g of sawdust using a pulverizer and pass it through a 100-mesh sieve. Soak the crushed sawdust in 1400g of alkaline solution for 2 hours. The alkaline solution is a sodium hydroxide solution with a sodium hydroxide concentration of 1mol / L. The alkaline solution also contains 3-aminopropyltriethoxysilane with a 3-aminopropyltriethoxysilane concentration of 1wt%. Centrifuge and filter the solution. Freeze-dry the product at -65℃ for 20 hours. S102. 60g of sawdust treated in step S101 is soaked in a mixed solution of 1300g hydrogen peroxide and sodium hypochlorite for 4 hours. The concentration of hydrogen peroxide is 10wt% and the concentration of sodium hypochlorite is 0.15mol / L. The filtered product is continuously treated with ozone at a concentration of 40ppm for 0.8 hours. During the ozone treatment, heating is carried out at a temperature of 80℃. S103. Add 50g of sawdust treated in step S102 to 250g of deionized water, then add 6g of modified mesoporous silica, continuously ultrasonically disperse for 1.5h, and then rotary evaporate at 70℃ to obtain modified sawdust. The preparation method of the above-mentioned modified fiber includes the following steps: S201. Disperse 70g of short-cut carbon fibers in 700g of acetone and heat under reflux at 80℃ for 18h. Then filter, wash the product with sufficient deionized water and dry it at 50℃. S202. Impregnate 60g of short-cut carbon fibers treated in step S201 into a Tris-HCl buffer solution containing dopamine hydrochloride at pH 8.5. The amount of dopamine hydrochloride is 24g and the amount of Tris-HCl buffer solution is 3250g. Place the solution on a shaker and shake for 24h at a shaking speed of 300rpm / min. Then filter the solution, wash the product with sufficient deionized water and dry it at 80℃. The method for preparing modified mesoporous silica in step S103 above includes the following steps; S301. Place 12g of silica with mesopores of 400nm into a muffle furnace and calcine at 400℃ for 5h. S302. Disperse the mesoporous silica calcined in step S301 into a 2 mol / L calcium chloride solution and soak for 2.5 h. The amount of calcium chloride solution used is 300 g. Then filter and dry the filtered product at 50 °C. S303. The mesoporous silica treated in step S302 is added to a deionized aqueous solution of oxidized starch. The amount of oxidized starch is 8g and the amount of deionized water is 120g. Then, the mixture is spray-dried to obtain modified mesoporous silica.

[0020] Example 2 A method for preparing green material for backfilling dike inlet holes, the method comprising the following steps: S1. Disperse 20g of modified fiber and 30g of modified sawdust into 600g of deionized water and stir continuously for 1 hour to obtain a mixture; S2. Add 210g of cement, 35g of bentonite and 600g of clay to the mixture obtained in step S1, and continue mixing for 0.5h to obtain the green material for backfilling the cofferdam inlet.

[0021] The modified sawdust described above was prepared by the following steps: S101. Crush 70g of sawdust using a pulverizer and pass it through a 100-mesh sieve. Soak the crushed sawdust in 1400g of alkaline solution for 1 hour. The alkaline solution is a sodium hydroxide solution with a sodium hydroxide concentration of 1mol / L. The alkaline solution also contains 3-aminopropyltriethoxysilane with a 3-aminopropyltriethoxysilane concentration of 1wt%. Centrifuge and filter the solution. Freeze-dry the product at -40℃ for 12 hours. S102. Soak 60g of sawdust treated in step S101 in a mixed solution of 1200g hydrogen peroxide and sodium hypochlorite for 1 hour. The concentration of hydrogen peroxide is 10wt% and the concentration of sodium hypochlorite is 0.15mol / L. Filter the product and treat it continuously with ozone at a concentration of 40ppm for 0.5 hours. During the ozone treatment, heating is carried out at a temperature of 80℃. S103. Add 50g of sawdust treated in step S102 to 300g of deionized water, then add 10g of modified mesoporous silica, continuously ultrasonically disperse for 1h, and then rotary evaporate at 70℃ to obtain modified sawdust. The preparation method of the above-mentioned modified fiber includes the following steps: S201. Disperse 70g of short-cut carbon fibers in 700g of acetone and heat under reflux at 80℃ for 18h. Then filter, wash the product with sufficient deionized water and dry it at 50℃. S202. Impregnate 60g of short-cut carbon fibers treated in step S201 into a Tris-HCl buffer solution containing 12g of dopamine hydrochloride at pH 8.5. The amount of Tris-HCl buffer solution used is 3000g. Place the solution on a shaker and shake for 24h at a shaking speed of 300rpm / min. Then filter the solution, wash the product with sufficient deionized water and dry it at 80℃. The method for preparing modified mesoporous silica in step S103 above includes the following steps; S301. Place 12g of silica with mesopores of 200nm into a muffle furnace and calcine at 350℃ for 5h. S302. Disperse the mesoporous silica after calcination in step S301 into a 2 mol / L calcium chloride solution and soak it for 2 hours. The amount of calcium chloride solution used is 300 g. Then filter it and dry the filtered product at 50°C. S303. The mesoporous silica treated in step S302 is added to a deionized aqueous solution of oxidized starch. The amount of oxidized starch is 12g and the amount of deionized water is 120g. Then, the mixture is spray-dried to obtain modified mesoporous silica.

[0022] Example 3 A method for preparing green material for backfilling dike inlet holes, the method comprising the following steps: S1. Disperse 60g of modified fiber and 50g of modified sawdust into 660g of deionized water and stir continuously for 1 hour to obtain a mixture; S2. Add 330g of cement, 45g of bentonite and 700g of clay to the mixture obtained in step S1, and continue mixing for 0.5h to obtain the green material for backfilling the cofferdam inlet.

[0023] The modified sawdust described above was prepared by the following steps: S101. Crush 70g of sawdust using a pulverizer and pass it through a 100-mesh sieve. Soak the crushed sawdust in 1400g of alkaline solution for 3 hours. The alkaline solution is a sodium hydroxide solution with a sodium hydroxide concentration of 1mol / L. The alkaline solution also contains 3-aminopropyltriethoxysilane with a 3-aminopropyltriethoxysilane concentration of 1wt%. Centrifuge and filter the solution. Freeze-dry the product at -80℃ for 24 hours. S102. 60g of sawdust treated in step S101 is soaked in a mixed solution of 1800g hydrogen peroxide and sodium hypochlorite for 5h. The concentration of hydrogen peroxide is 10wt% and the concentration of sodium hypochlorite is 0.15mol / L. The filtered product is continuously treated with ozone at a concentration of 40ppm for 1h. During the ozone treatment, heating is carried out at a temperature of 80℃. S103. Add 50g of sawdust treated in step S102 to 225g of deionized water, then add 5g of modified mesoporous silica, continuously ultrasonically disperse for 2h, and then rotary evaporate at 70℃ to obtain modified sawdust. The preparation method of the above-mentioned modified fiber includes the following steps: S201. Disperse 70g of short-cut carbon fibers in 700g of acetone and heat under reflux at 80℃ for 18h. Then filter, wash the product with sufficient deionized water and dry it at 50℃. S202. Impregnate 60g of short-cut carbon fibers treated in step S201 into a Tris-HCl buffer solution containing 60g of dopamine hydrochloride at pH 8.5. The amount of Tris-HCl buffer solution used is 4200g. Place the solution on a shaker and shake for 24h at a shaking speed of 300rpm / min. Then filter the solution, wash the product with sufficient deionized water, and dry it at 80℃. The method for preparing modified mesoporous silica in step S103 above includes the following steps; S301. Place 12g of silica with mesopores of 500nm into a muffle furnace and calcine at 500℃ for 5h. S302. Disperse the mesoporous silica calcined in step S301 into a 2 mol / L calcium chloride solution and soak it for 3 hours. The amount of calcium chloride solution used is 300 g. Then filter it and dry the filtered product at 50°C. S303. The mesoporous silica treated in step S302 is added to a deionized aqueous solution of oxidized starch. The amount of oxidized starch is 6g and the amount of deionized water is 120g. Then, the mixture is spray-dried to obtain modified mesoporous silica.

[0024] Example 4 A method for preparing green material for backfilling dike inlet holes, the method comprising the following steps: S1. Disperse 45g of modified fiber and 35g of modified sawdust into 650g of deionized water and stir continuously for 1 hour to obtain a mixture; S2. Add 310g of cement, 42g of bentonite and 680g of clay to the mixture obtained in step S1, and continue mixing for 0.5h to obtain the green material for backfilling the cofferdam inlet.

[0025] The modified sawdust described above was prepared by the following steps: S101. Crush 70g of sawdust using a pulverizer and pass it through a 100-mesh sieve. Soak the crushed sawdust in 1400g of alkaline solution for 2.5h. The alkaline solution is a sodium hydroxide solution with a sodium hydroxide concentration of 1mol / L. The alkaline solution also contains 3-aminopropyltriethoxysilane with a 3-aminopropyltriethoxysilane concentration of 1wt%. Centrifuge and filter the solution. Freeze-dry the product at -50℃ for 22h. S102. 60g of sawdust treated in step S101 is soaked in a mixed solution of 1500g hydrogen peroxide and sodium hypochlorite for 3 hours. The concentration of hydrogen peroxide is 10wt% and the concentration of sodium hypochlorite is 0.15mol / L. The filtered product is continuously treated with ozone at a concentration of 40ppm for 0.5 hours. During the ozone treatment, heating is carried out at a temperature of 80℃. S103. Add 50g of sawdust treated in step S102 to 270g of deionized water, then add 8g of modified mesoporous silica, continuously ultrasonically disperse for 1.5h, and then rotary evaporate at 70℃ to obtain modified sawdust. The preparation method of the above-mentioned modified fiber includes the following steps: S201. Disperse 70g of short-cut carbon fibers in acetone and heat under reflux at 80°C for 18h. Then filter, wash the product with sufficient deionized water and dry at 50°C. S202. Impregnate 60g of short-cut carbon fibers treated in step S201 into a Tris-HCl buffer solution containing 30g of dopamine hydrochloride at pH 8.5. The amount of Tris-HCl buffer solution used is 1900g. Place the solution on a shaker and shake for 24h at a shaking speed of 300rpm / min. Then filter the solution, wash the product with sufficient deionized water, and dry it at 80℃. The method for preparing modified mesoporous silica in step S103 above includes the following steps; S301. Place 12g of silica with mesopores of 400nm into a muffle furnace and calcine at 450℃ for 5h. S302. Disperse the mesoporous silica calcined in step S301 into a 2 mol / L calcium chloride solution and soak it for 3 hours. The amount of calcium chloride solution used is 300 g. Then filter it and dry the filtered product at 50°C. S303. The mesoporous silica treated in step S302 is added to a deionized aqueous solution of oxidized starch. The amount of oxidized starch is 9g and the amount of deionized water is 110g. Then, the mixture is spray-dried to obtain modified mesoporous silica.

[0026] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the treatment process of sawdust through a mixed solution of hydrogen peroxide and sodium hypochlorite in step S102 is omitted, while the remaining steps are exactly the same as in Example 1.

[0027] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the ozone treatment of sawdust in step S102 is omitted, while the remaining steps are exactly the same as in Example 1.

[0028] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the mesoporous silica loaded with calcium ions added in step S103 is replaced with mesoporous silica without calcium ions, that is, the step of soaking the mesoporous silica in calcium chloride solution after calcination is eliminated. The remaining steps are exactly the same as in Example 1.

[0029] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the addition of mesoporous silica in step S103 was completely eliminated. Instead, the same weight of mesoporous silica loaded with calcium ions was added along with cement, bentonite and clay in step S2. The remaining steps were exactly the same as in Example 1.

[0030] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that step S202 was completely eliminated, that is, the coating of polydopamine on the surface of the short-cut carbon fibers was eliminated. The remaining steps are exactly the same as those in Example 1.

[0031] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that in step S202, after the short-cut carbon fibers are impregnated with the Tris-HCl buffer solution, the shaking step is cancelled and replaced with standing. The remaining steps are exactly the same as in Example 1.

[0032] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that step S303 is completely omitted, while the remaining steps are exactly the same as in Example 1.

[0033] The cement used in the above embodiments is P.O32.5 grade ordinary Portland cement produced by Gansu Qilianshan Cement Group Co., Ltd., and its chemical composition is shown in Table 1 below: Table 1: Chemical Composition of Ordinary Portland Cement The bentonite used in the above embodiments is natural sodium-based bentonite produced in Gongyi City, and its various indicators should meet the requirements of the standard "Bentonite" (GB / T 20973-2007); The clay used in this invention was tested according to the "Standard for Geotechnical Testing Methods" (GBT50123-1999), and some of the test results are shown in Table 2 below: Table 2: Physical Properties of Clay In the particle composition of clay, particles ≥0.075mm account for 13%, particles 0.075-0.005mm account for 65%, and particles ≤0.005mm account for 22%.

[0034] Eleven sets of green materials for backfilling cofferdam boreholes were prepared through Examples 1-4 and Comparative Examples 1-7. After these eleven sets of green materials had set for 3, 5, and 28 days, compressive strength tests were conducted. In accordance with the "Specification for Cement-Soil Mix Design" (JGJ / T 233-2011), the compressive strength test specimens were molded using standard cubic molds measuring 70.7mm × 70.7mm × 70.7mm. The compressive strength test results are shown in Table 3 below. Table 3: Compressive strength test results of the green materials for backfilling cofferdam inlet holes prepared in Examples 1-4 and Comparative Examples 1-7 at 3, 5, and 28 days. In Table 3 above, Comparative Examples 1-2 reduced the oxidation treatment step on the sawdust surface, thus reducing the provision of active sites. This weakened the bond between mesoporous silica and sawdust, resulting in a significant decrease in compressive strength. In Comparative Example 4, the mesoporous silica was directly dispersed into the backfill material, which reduced its dispersion performance and the corresponding pozzolanic effect, further weakening the compressive strength. In Comparative Example 3, calcium ions were loaded into the mesoporous silica, and these ions were released to replenish the reaction system, improving the hydration effect and enhancing the overall strength of the material. In Comparative Example 7, the process of drying and spraying oxidized starch and mesoporous silica together was eliminated. Due to the loss of the effect of oxidized starch in enhancing the bond between mesoporous silica and sawdust, and the fact that oxidized starch could delay the exposure of mesoporous silica in an alkaline environment, the compressive strength at 5 and 28 days decreased.

[0035] According to the "Specification for Cement-Soil Mix Design" (JGJ / T 233-2011), the green material for backfilling the 10 sets of cofferdam boreholes was molded using standard cube molds measuring 70.7mm×70.7mm×70.7mm. After 5 days of setting, samples were taken using a ring cutter with a diameter of 61.8mm and a height of 20mm, and then a direct shear test was conducted. The tested cohesion is shown in Table 4 below. Table 4: Cohesion test results of the green materials for backfilling cofferdam inlet holes prepared in Examples 1-4 and Comparative Examples 1-7 after 5 days. Compared with Example 1, the cohesive strength of Comparative Examples 1-4 in Table 4 above decreased, mainly due to the uneven dispersion of mesoporous silica and the weakened bonding with sawdust, which led to a weakened pozzolanic reaction and a weakened overall hydration reaction of the material. Comparative Example 7 also showed a decrease compared to Example 1. Due to the lack of interaction with oxidized starch, the bonding ability between mesoporous silica and sawdust decreased, the dispersion effect was not as good as in Example 1, and the cohesive strength also decreased. The cohesive strength of Comparative Examples 5-6 decreased significantly compared to Example 1. In Comparative Example 4, the removal of polydopamine weakened the bonding ability between chopped carbon fibers and sawdust and other materials. In Example 5, the removal of the shaking table reduced the surface roughness of polydopamine, decreased its mechanical interlocking ability, and also reduced the cohesive strength.

[0036] 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 cofferdam for inducing backfilling of green material, characterized in that, Materials comprising the following components by weight: 21-33 parts cement, 3.5-4.5 parts bentonite, 60-70 parts clay, 3-5 parts modified sawdust, 60-66 parts deionized water, and 2-6 parts modified fiber; The modified sawdust is prepared by the following steps: S101. Crush the sawdust using a pulverizer and pass it through a 100-mesh sieve. Soak the crushed sawdust in an alkaline solution for 1-3 hours, centrifuge and filter, and freeze-dry the product at -40 to -80°C for 12-24 hours. S102. The sawdust treated in step S101 is soaked in a mixed solution of hydrogen peroxide and sodium hypochlorite for 1-5 hours. The filtered product is then continuously treated with ozone at a concentration of 40 ppm for 0.5-1 hours. During the ozone treatment, the product is heated at a temperature of 80°C. S103. Add the sawdust treated in step S102 to deionized water, then add modified mesoporous silica, continuously ultrasonically disperse for 1-2 hours, and then rotary evaporate at 70°C to obtain modified sawdust. The modified fiber is a short-cut carbon fiber coated with polydopamine; The method for preparing the modified fiber includes the following steps: S201. Disperse short-cut carbon fibers in acetone and heat under reflux at 80°C for 18 hours. Then filter the mixture, wash the product with sufficient deionized water and dry it at 50°C. S202. The short-cut carbon fibers treated in step S201 are impregnated in a Tris-HCl buffer solution containing dopamine hydrochloride at pH 8.5 and shaken on a shaker for 24 hours at a shaking speed of 300 rpm / min. After that, the mixture is filtered, washed with sufficient deionized water, and dried at 80°C.

2. The cofferdam green material of claim 1, wherein, The method for preparing modified mesoporous silica in step S103 includes the following steps; S301. Place the mesoporous silica in a muffle furnace and calcine it at 350~500℃ for 5 hours; S302. Disperse the mesoporous silica calcined in step S301 into a calcium chloride solution and soak it for 2-3 hours. Then filter it and dry the filtered product at 50°C. S303. The mesoporous silica treated in step S302 is added to a deionized aqueous solution of oxidized starch, and then spray-dried to obtain modified mesoporous silica.

3. The cofferdam drawdown backfill green material of claim 1, wherein, The alkaline solution in step S101 is a sodium hydroxide solution with a concentration of 1 mol / L; the alkaline solution also contains 3-aminopropyltriethoxysilane with a concentration of 1 wt%.

4. The cofferdam drawdown backfill green material of claim 1, wherein, In step S102, the concentration of hydrogen peroxide is 10 wt% and the concentration of sodium hypochlorite is 0.15 mol / L; the mass ratio between the sawdust treated in step S101 and the mixed solution of hydrogen peroxide and sodium hypochlorite is 1:(20~30).

5. The cofferdam lead-in backfill green material according to claim 2, wherein, In step S103, the mass ratio of modified mesoporous silica, deionized water and sawdust treated in step S102 is 1:(30~45):(5~10).

6. The green material for backfilling the cofferdam pilot hole according to claim 2, characterized in that, The particle size of the mesoporous silica in step S301 is 200~500nm, and the concentration of the calcium chloride solution in step S302 is 2mol / L.

7. The green material for backfilling the cofferdam pilot hole according to claim 2, characterized in that, In step S303, the mass ratio of oxidized starch to deionized water is 1:(10-20), and the mass ratio of oxidized starch to mesoporous silica in step S301 is 1:(1-2).

8. The green material for backfilling the cofferdam pilot hole according to claim 1, characterized in that, In step S202, the mass ratio of short-cut carbon fibers, dopamine hydrochloride, and Tris-HCl buffer is 1:(0.2~1):(50~70).

9. A method for the preparation of a cofferdam for the reclamation of green areas according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: S1. Disperse the modified fiber and modified sawdust into deionized water according to the mass parts, and stir continuously for 1 hour to obtain a mixture; S2. Add cement, bentonite and clay to the mixture obtained in step S1 according to the mass ratio, and continue mixing for 0.5 hours to obtain the green material for backfilling the cofferdam inlet.

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