A composite cement soil prepared from seawater, nano-silica and polyvinyl alcohol fiber and a preparation method thereof

Abstract

The application belongs to the technical field of cement soil preparation, and particularly relates to a composite cement soil prepared from seawater, nano-silicon dioxide and polyvinyl alcohol fiber and a preparation method thereof, which comprises 63-70% of dry soil powder, 9-10% of Portland cement, 1.8-2.2% of nano-silicon dioxide, 0.6-1.2% of polyvinyl alcohol fiber, 0.2% of dispersant and 16.4-25.4% of seawater. The composite cement soil can not only significantly reduce the dependence on fresh water resources, but also effectively solve the problems of seawater corrosion and deterioration caused by fatigue cracks due to long-term cyclic loading, thereby significantly improving the mechanical strength of the cement soil foundation and prolonging the service life of the cement soil foundation in the coastal environment, and the composite cement soil also has high economic benefits. The synergistic effect of the nano-silicon dioxide and the polyvinyl alcohol fiber significantly enhances the mechanical properties, crack resistance and seawater corrosion resistance of the cement soil, and effectively inhibits the brittle failure of the cement soil, so that the cement soil can be stably applied in the coastal soft soil foundation reinforcement engineering for a long time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of cement soil preparation, and particularly relates to a composite cement soil prepared from seawater, nano-silicon dioxide and polyvinyl alcohol fiber and a preparation method thereof. BACKGROUND

[0002] The mixing water required in the production process of traditional cement mixing piles consumes a large amount of fresh water. If the water used in the aspects of cooling, washing, energy and transportation is taken into account, the fresh water consumption in the entire manufacturing process will be several times more than that. In remote coastal areas and islands where fresh water resources are scarce, long-distance transportation of fresh water not only significantly increases the cost, but also increases energy consumption. In addition, in order to cope with the shortage of fresh water, a temporary water supply system needs to be established, which not only prolongs the construction time, but also may cause unnecessary delays in the construction process.

[0003] In the coastal port traffic subgrade of remote coastal areas and island reef areas, the cement-based material is gradually eroded by periodic loads (such as traffic vehicle driving or machine vibration) and corrosive ions in seawater, which may gradually form fatigue cracks. Although these cracks may have little effect on the overall structure of the cement soil foundation in the short term, under the coupling effect of long-term cyclic load and corrosion degradation, the tiny cracks will gradually expand and penetrate, eventually leading to the destruction of the pile body, which seriously endangers the normal use and engineering safety. Although increasing the cement content can alleviate these problems to some extent, it may cause new problems such as uneven strength of the cement soil foundation, prolonged maintenance period and increased brittleness. These problems not only increase the construction difficulty and cost, but also significantly reduce the safety of the cement soil foundation. In addition, large-scale production of cement will also cause a large amount of CO2 emission. Therefore, solving the problems of easy cracking, easy degradation, insufficient strength and environmental pollution of cement soil is the key to realizing its long-term stable application in coastal areas and island reef areas.

[0004] Currently, there are some solutions to the above problems. For example, patent CN103539389B provides a method for preparing cement soil using seawater, which replaces fresh water to reduce the use of fresh water and inhibits the influence of corrosive ions in the ocean. However, this method has limited effect on improving the strength of cement soil, and does not consider the defect that cement soil is prone to cracking when subjected to cyclic loading, which will accelerate its deterioration process. In addition, this technology needs to add a large amount of corrosion inhibitor, which not only increases the construction time and cost, but also may cause certain safety hazards. "Test on dynamic elastic modulus and damping ratio of cement soil modified by nano-SiO2 in corrosive environment" (Engineering Science and Technology, Zhuang Xinshen et al., 2024) and patent CN112851247B disclose a method for improving the seawater corrosion resistance and fatigue performance of cement soil by adding nano-silicon dioxide in the cement soil. However, this method also exacerbates the tendency of brittle failure of cement soil when subjected to ultimate load in seawater environment, which may cause major safety hazards. Patent CN114292080A and "Bending and early anti-cracking performance of jute and polyvinyl alcohol fiber reinforced cement soil" (Bulletin of the Chinese Ceramic Society, Yao Xin et al., 2021, 40(09)) disclose a method for improving the anti-cracking performance of cement soil and preventing brittle failure by using polyvinyl alcohol fiber. However, this method has limited effect on improving the strength of cement soil, and the separate application of polyvinyl alcohol fiber is greatly limited in seawater environment.

[0005] Therefore, how to provide an anti-corrosion cement soil with high strength, high durability and high safety using seawater as the water source has become a technical problem to be solved. SUMMARY

[0006] The purpose of the present application is to provide a composite cement soil prepared from seawater, nano-silicon dioxide and polyvinyl alcohol fiber and a preparation method thereof, which obtains high-strength and anti-cracking and anti-corrosion cement soil by formula optimization using seawater as the water source.

[0007] To achieve the above-mentioned purpose, the present application provides a composite cement soil prepared from seawater, nano-silicon dioxide and polyvinyl alcohol fiber, the raw materials of which include, by mass percentage, 63-70% of dry soil powder, 9-10% of Portland cement, 1.8-2.2% of nano-silicon dioxide, 0.6-1.2% of polyvinyl alcohol fiber, 0.2% of dispersant and 16.4-25.4% of seawater.

[0008] Further, the particle size of the nano-silicon dioxide is 20±5nm, and the specific surface area is 160-190m 2 / g.

[0009] Further, the polyvinyl alcohol fiber has a length of 6±1mm, an equivalent diameter of 16±1pm and a density of 1.29±0.1g / cm 3 .

[0010] Further, the mass ratio of sea salt to fresh water in the seawater is (32-38):1000, preferably 35:1000. In actual engineering, the pre-seawater treatment process is as follows: first, seawater is extracted, and a first step of filtration operation is performed through a large grid, and then a second step of filtration is performed using a small grid. Subsequently, the seawater after two times of filtration is introduced into a sedimentation tank for sedimentation treatment. When there is no obvious floating matter in the seawater, the supernatant is introduced into a water storage tank, and thus the pretreatment of seawater is completed.

[0011] Further, the dispersant is polyvinylpyrrolidone K30.

[0012] And / or, the Portland cement is P.O 42.5 Portland cement.

[0013] Further, the dry soil powder is obtained by uniformly spreading the collected original soil sample at a depth of 15±1m underground, and placing it outdoors for natural evaporation for 40-50 hours. After natural evaporation, the soil sample is crushed and dried in an oven at 105±5℃ for 20-30 hours, and then cooled and passed through a 2mm sieve to obtain the dry soil powder.

[0014] The application also provides a preparation method of the composite cement soil prepared from seawater, nano-silicon dioxide and polyvinyl alcohol fiber according to any one of the above, and the preparation steps are as follows:

[0015] (1) The dry soil powder, polyvinyl alcohol fiber, nano-silicon dioxide, cement and dispersant are weighed according to the proportion, and then stirred in a blender for 6-8 minutes until uniformly mixed;

[0016] (2) The required mass of seawater is weighed and poured into the mixture in the blender, and continues to be stirred for 10-12 minutes until the mixture forms a uniform cement slurry;

[0017] (3) The uniformly mixed cement slurry is poured into a mold, and during the grouting process, the mold is placed on a vibration table to keep vibrating until the mold is filled with cement slurry and air bubbles are removed;

[0018] (4) After curing at 20℃±2℃ for 48 hours, the mold is demolded to obtain the composite cement soil.

[0019] Further, the mold is a cylindrical transparent plastic mold with a diameter of 39mm and a height of 78mm.

[0020] Further, the polyvinyl alcohol fiber is dispersed by ultrasonic vibration screen treatment technology before being added.

[0021] The application also provides the application of the composite cement soil prepared from seawater, nanosilica and polyvinyl alcohol fibers.

[0022] The application uses seawater instead of fresh water to prepare the composite cement soil, and effectively solves the engineering practical problems of fresh water resource shortage in remote island reef areas by local material.

[0023] Compared with the prior art, the above technical scheme has the following technical advantages and beneficial effects:

[0024] 1. In view of the poor corrosion resistance, poor crack resistance, low strength growth rate and brittle failure of the existing seawater cement soil reinforcement scheme, the composite cement soil prepared from seawater, nanosilica and polyvinyl alcohol fibers effectively solves the above problems. By adding nanosilica and polyvinyl alcohol fiber composite material, the hydration reaction of cement can be improved, and the good combination of fiber and cement soil matrix can be promoted, so that the reinforcing effect of nanosilica and fiber can be fully played. The application significantly reduces the dependence on fresh water resources, effectively solves the problems of seawater corrosion and fatigue cracks caused by long-term cyclic loading, and greatly improves the mechanical strength and service life of the cement soil in the coastal environment.

[0025] 2. In the composite cement soil of the application, nanosilica and the hydration products generated by promoting it effectively fill the internal pores of the cement soil, greatly enhance the chain effect between the fiber and the cement soil matrix, thereby inhibiting the corrosion of seawater on the internal structure of the cement soil, and effectively improving the deformation and settlement problems of the cement soil in the coastal environment. The application has the advantages of reliable technology, reasonable design, no environmental pollution, strong adaptability and convenient construction.

[0026] 3. Through a large number of experiments, the optimal material ratio and preparation method of the cement soil prepared from seawater, nanosilica and polyvinyl alcohol fiber composite material are determined. Only by using the optimal dosage and preparation method of the application, the strength growth rate of the composite cement soil prepared from nanosilica and polyvinyl alcohol fiber can exceed the sum of the strength growth rates of single fiber cement soil and single nanosilica cement soil, and the best solidification effect can be achieved, thereby meeting the requirements of long-term mechanical stability of the project.

[0027] 4、The composite cement soil of the present application provides a new technical idea and reference for the construction of coastal traffic subgrade and pile foundation in remote coastal and island areas. The application of nano-silicon dioxide and polyvinyl alcohol fiber in cement soil is the first time. The improvement effect and economic benefit of the polyvinyl alcohol fiber used in seawater environment on cement soil are significantly better than those of glass fiber, basalt fiber, steel fiber and polypropylene fiber and other similar materials. As a hydrophilic fiber, polyvinyl alcohol fiber has stronger bonding force with cementitious materials and superior performance in compression ductility, effectively reducing the risk of brittle failure of cement soil.

[0028] Compared with the prior art, the technical solution proposed in the present application has the following advantages:

[0029] Compared with the patent CN103539389B, the patent does not consider the defect that cement soil is prone to cracking under cyclic load, which will accelerate its deterioration process. This technology needs to add a large amount of corrosion inhibitor, and a large amount of corrosion inhibitor may form too many pores or microcracks in the cement soil, not only reducing the impermeability, but also changing the pore structure of the cement soil, increasing the porosity and changing the pore size distribution, and increasing the number of large pores. This will not only affect the mechanical properties and durability of the cement soil, but also the corrosion inhibitor may contain some harmful chemicals to the environment, such as heavy metal ions, organic matter, etc. When the cement soil is subjected to rainwater erosion or other natural factors during use, these harmful substances may gradually be released, causing pollution to the surrounding soil and water environment and affecting the ecological balance. At the same time, the patent also has the defects of low strength and poor durability of cement soil. In view of the fact that the existing seawater cement soil reinforcement scheme cannot be directly applied and has deficiencies, the reinforced cement soil material selected in the present application has greater advantages. The addition of polyvinyl alcohol fiber in the cement soil prepared by adding nano-silicon dioxide and polyvinyl alcohol fiber composite material can further improve the strength and effectively improve the crack resistance of the cement soil.

[0030] The present application is compared with "Nano-SiO2 Improved Cement Soil Dynamic Elastic Modulus and Damping Ratio Test in Corrosive Environment" (Engineering Science and Technology, Zhuang Xinshen et al., 2024) and "Patent CN112851247B Anti-seawater Corrosion Nano-cement Soil and Its Preparation Method", the price of single nano-silicon dioxide improved cement soil is higher, and the single nano-silicon dioxide improved cement soil has poor crack resistance, which aggravates the trend of brittle failure of cement soil under ultimate load in seawater environment, thereby possibly causing major safety hazards, the present application is configured by adding nano-silicon dioxide and polyvinyl alcohol fiber composite material, the fiber surface in the composite cement soil is wrapped by more and denser calcium silicate gel, thereby enhancing the material mechanical interlocking effect between the fiber and the hydration product. When the fiber is compressed, the sharp soil particles exert pressure on the fiber surface, forming a dent structure. The incorporation of nano-silicon dioxide can effectively prevent the sliding and recombination of soil particles and further increase the roughness of the fiber surface. The present application greatly enhances the mechanical interlocking effect between the fiber and the hydration product, fills the capillary structure of the cement soil, enhances the internal structure, eliminates the corrosion of the internal structure by seawater, greatly enhances the corrosion resistance, crack resistance and mechanical strength of the cement soil, and reduces the required cost.

[0031] Compared with patent CN114292080A and "Hemp and Polyvinyl Alcohol Fiber Reinforced Cement Soil Bending and Early Anti-cracking Performance" (Bulletin of the Chinese Ceramic Society, Yao Xin et al., 2021, 40 (09)), although polyvinyl alcohol fiber can improve the tensile strength and toughness of cement soil to some extent, the improvement effect on the compressive strength of cement soil is relatively limited. The disadvantage of single addition of polyethylene fiber is that when the hydration product is insufficient, the fiber is difficult to form effective bonding with the cement soil matrix, thereby limiting the full play of the fiber function. In some engineering applications with high requirements for cement soil compressive strength, such as foundation bearing layer, etc., the engineering requirements may not be met. In view of the defect that the fiber function cannot be fully played in the patent, the present application can effectively improve the hydration reaction of cement by adding nano-silicon dioxide, promote the good combination of fiber and cement soil matrix, and fully play the reinforcing effect of fiber. The present application also finds, through a large number of experiments, cement soil based on seawater, nano-silicon dioxide and polyvinyl alcohol fiber composite material, through the optimal material ratio and preparation method, the cement soil solidification strength is improved, the long-term mechanical stability requirement of engineering is met, the present application has the advantages of technical reliability and reasonableness, no pollution to environment, strong adaptability, convenient construction and the like.

[0032] The present application also conducts in-depth feasibility analysis on the erosion and damage of corrosive ions in seawater to cement soil:

[0033] The composite addition of nano-silica and polyvinyl alcohol fiber makes the cement soil structure more compact, prevents the invasion of chemical corrosion medium, and at the same time, the two have certain chemical stability, can improve the resistance of cement soil to acid, alkali and salt and other chemicals to a certain extent, and the combined action of the two can significantly improve the impermeability of cement soil, reduce the erosion risk of external moisture, salt and the like to cement soil, and the polyvinyl alcohol fiber can limit the shrinkage deformation of cement soil and reduce the generation of shrinkage cracks. The filling effect of nano-silica also helps to reduce the shrinkage rate of cement soil, and the synergistic effect of the two can effectively control the formation and development of cement soil cracks.

[0034] In summary, the present application effectively solves the defects of the prior art. And through a large number of experiments, the optimal ratio of fiber and nano-silica is determined, which avoids the influence of the performance of the combined application of the two due to excessive or insufficient addition, and only when the optimal amount of materials determined by the present application and the corresponding preparation method are used, can the strength growth rate of the composite cement soil prepared by nano-silica and polyvinyl alcohol fiber exceed the sum of the growth rates of single fiber cement soil and single nano cement soil. Only by using the optimal amount of materials determined by the present application and the corresponding preparation method, can the best solidification effect be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The figure is a schematic diagram of the distribution of nano-silica and fiber in the composite cement soil of the present application in the cement soil.

[0036] Figure 2 The figure is a schematic diagram of the micro-interface mechanics of nano-silica and fiber in the composite cement soil of the present application.

[0037] REFERENCE NUMERALS

[0038] 1-Universal testing machine, 2-Cement soil, 3-Fiber, 4-Stress around the fiber, 5-Pore water, 6-Indentation on the surface of the fiber, 7-Friction and cohesion between the fiber and the hydration product, 8-Pore, 9-Hydration product of nano-silica, 10-Fiber fracture, 11-Soil particle, 12-Matrix, 13-Tensile stress, 14-Sharp soil particle, 15-Resistance provided by nano-particle and hydration product, 16-Rotation of soil particle; 21-Fiber, 22-Addition of nano-silica, 23-Fiber pulled out state, 24-Nano-silica filling pores and pore water, 25-Fiber fracture. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0040] The technical problem to be solved by the present application is how to realize local material procurement, overcome the influence of corrosion ions in seawater in the application process, ensure that the prepared cement soil has high strength, and significantly improve its service life and safety. To this end, the present application provides a composite cement soil prepared from seawater, nano-silicon dioxide and polyvinyl alcohol fiber, and the raw materials include, by mass percentage: dry soil powder 63-70%, silicate cement 9-10%, nano-silicon dioxide 1.8-2.2%, polyvinyl alcohol fiber 0.6-1.2%, dispersant 0.2%, and seawater 16.4-25.4%. In remote island areas, not only can the dependence on fresh water resources be significantly reduced, but also the problems of seawater corrosion and deterioration caused by fatigue cracks under long-term cyclic loading can be effectively solved, thereby significantly improving the service life of the cement soil foundation in the coastal environment and greatly enhancing the corrosion resistance, crack resistance and mechanical strength of the cement soil. The method has excellent economic benefits, can effectively meet the actual production needs, and has the advantages of local material procurement, simple process and convenient operation.

[0041] In combination Figure 1 and Figure 2 It can be seen that the anti-cracking and anti-corrosion principle of the present application is as follows:

[0042] The polyvinyl alcohol fiber improves the crack resistance of the cement soil and inhibits brittle failure through the bonding force between the fiber and the cement soil matrix; the nano-silicon dioxide relies on its pozzolanic activity and nucleation effect to promote cement hydration, thereby enhancing the mechanical properties and corrosion resistance of the cement soil. However, when the cement soil with only added fiber is subjected to fracture failure during loading, the pores and pore water around the fiber will weaken the frictional resistance between the matrix and the fiber, making it lower than the tensile stress borne by the fiber, causing the fiber to easily slide out and lose the "bridge" effect of connecting the cracks of the cement soil. In addition, the fracture failure of the fiber due to the lack of effective wrapping of the matrix is also one of the main reasons for further reducing the strength of the cement soil.

[0043] The present application can effectively solve the above problems by adding polyvinyl alcohol fibers and nano-silica to prepare a composite cement soil. When the fibers are compressed, the surface of the fibers is indented due to the extrusion of sharp soil particles. The incorporation of nano-silica not only fills the pores of the cement soil, but also promotes cement hydration, generating more and denser calcium silicate gel embedded in the surface of the fibers and their indentations, thereby effectively preventing the sliding and recombination of soil particles and further increasing the roughness of the fiber surface. The mechanical interlocking between the fibers and the matrix effectively prevents the fibers from being pulled out and broken under tensile and compressive stress, thereby significantly improving the compressive strength, residual strength, crack resistance, and seawater corrosion resistance of the cement soil. In addition, polyvinyl alcohol fibers have hydrophilic properties, with polar groups such as carboxyl (-COOH) and hydroxyl (-OH) on their surface, which can adsorb water molecules and form ionic bonds with calcium ions. Therefore, the interfacial shear failure of polyvinyl alcohol fibers mainly involves two forces: one is the frictional force between the fibers and the cement soil matrix, and the other is the mechanical force that breaks the chemical bond between the fibers and the matrix. The above characteristics make it more suitable for combined application with nano-silica to improve the performance of cement soil compared to other fibers.

[0044] The dry soil powder samples used in the following examples and comparative examples were taken from a construction site 15 meters underground in Hongshan District, Wuhan City, which has similar properties to marine soft soil.

[0045] The average particle size of the nano-silica is 20 nm, and the specific surface area is 160-190 m 2 / g, the length of the polyvinyl alcohol fiber is 6 mm, the equivalent diameter is 16 μm, and the density is 1.29 g / cm 3 The mass ratio of sea salt to fresh water in seawater is 35:1000 (usually requires filtration to remove insoluble impurities), the dispersant is polyvinylpyrrolidone K30, and the cement is P.O42.5 Portland cement.

[0046] Example 1

[0047] (1). The original soil was dried and crushed through a 2 mm sieve to obtain dry soil powder with a particle size of less than 2 mm.

[0048] (2). The dry soil powder obtained in step (1) was mixed with polyvinyl alcohol fiber 1.2%, nano-silica 1.9%, cement 9.0%, and dispersant 0.2% by mass percentage and poured into a blender and stirred for 6-8 minutes until evenly mixed.

[0049] (3). Before adding, the polyvinyl alcohol fiber needs to be dispersed by ultrasonic vibration sieve treatment technology to improve the uniformity of the polyvinyl alcohol fiber dispersion.

[0050] (4). Pour seawater (mass content according to Table 1) into the mixture in the blender, and continue to stir for 10-12 minutes until the mixture forms a uniform cement paste.

[0051] (5). Pour the uniformly mixed cement paste into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, place the mold on a vibration table and keep it vibrating until the mold is full and the air bubbles are removed.

[0052] (6). Label the sample number, and after 48 hours of curing at 20℃±2℃, demold to obtain the target product.

[0053] Example 2

[0054] (1). Dry and crush the original soil retrieved through a 2mm sieve to obtain dry soil powder with a particle size less than 2mm.

[0055] (2). Mix the dry soil powder obtained in step (1) 65.0%, polyvinyl alcohol fiber 0.8%, nano-silica 2.1%, cement 9.0%, and dispersant 0.2% by mass percentage, and introduce them into the blender and stir for 6-8 minutes until the mixture is uniform.

[0056] (3). The polyvinyl alcohol fiber needs to be dispersed by ultrasonic treatment before being added.

[0057] (4). Pour seawater (mass content according to Table 1) into the mixture in the blender, and continue to stir for 10-12 minutes until the mixture forms a uniform cement paste.

[0058] (5). Pour the uniformly mixed cement paste into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, place the mold on a vibration table and keep it vibrating until the mold is full and the air bubbles are removed.

[0059] (6). Label the sample number, and after 48 hours of curing at 20℃±2℃, demold to obtain the target product.

[0060] Example 3

[0061] (1). Dry and crush the original soil retrieved through a 2mm sieve to obtain dry soil powder with a particle size less than 2mm.

[0062] (2). Mix the dry soil powder obtained in step (1) 70.0%, polyvinyl alcohol fiber 1.0%, nano-silica 2.2%, cement 10.0%, and dispersant 0.2% by mass percentage, and introduce them into the blender and stir for 6-8 minutes until the mixture is uniform.

[0063] (3). The polyvinyl alcohol fiber needs to be dispersed by ultrasonic treatment before being added.

[0064] (4). Pour seawater (mass content according to Table 1) into the mixture in the blender, and continue to stir for 10-12 minutes until the mixture forms a uniform cement paste.

[0065] (5). Pour the uniformly mixed cement paste into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, place the mold on a vibration table and keep it vibrating until the mold is full and the air bubbles are removed.

[0066] (6). Label the sample number, and after 48 hours of curing at 20℃±2℃, demold to obtain the target product.

[0067] Comparative Example 1

[0068] (1). Dry and crush the original soil retrieved to pass through a 2mm sieve to obtain dry soil powder with a particle size less than 2mm.

[0069] (2). Mix the dry soil powder obtained in step (1) 63.0%, polyvinyl alcohol fiber 0.0%, nano-silica 0.0%, cement 9.0%, and dispersant 0.2% by mass percentage, and introduce them into a blender and stir for 6-8 minutes until they are uniformly mixed.

[0070] (3). Pour seawater (mass content according to Table 1) into the mixture in the blender, and continue to stir for 10-12 minutes until the mixture forms a uniform cement paste.

[0071] (4). Pour the uniformly mixed cement paste into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, place the mold on a vibration table and keep it vibrating until the mold is full and the air bubbles are removed.

[0072] (5). Label the sample number, and after 48 hours of curing at 20℃±2℃, demold to obtain the target product.

[0073] Comparative Example 2

[0074] (1). Dry and crush the original soil retrieved to pass through a 2mm sieve to obtain dry soil powder with a particle size less than 2mm.

[0075] (2). Mix the dry soil powder obtained in step (1) 63.0%, polyvinyl alcohol fiber 1.2%, nano-silica 0.0%, cement 9.0%, and dispersant 0.2% by mass percentage, and introduce them into a blender and stir for 6-8 minutes until they are uniformly mixed.

[0076] (3). Before adding, the polyvinyl alcohol fiber needs to be dispersed by ultrasonic treatment.

[0077] (4). Pour the mixed cement slurry into a transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, keep the mold on the vibration table to vibrate until the mold is full and the bubbles are removed.

[0078] (5). Pour the mixed cement slurry into a transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, keep the mold on the vibration table to vibrate until the mold is full and the bubbles are removed.

[0079] (6). Label the sample number and demold after 48 hours of curing at 20℃±2℃, and the target product is obtained.

[0080] Comparative Example 3

[0081] (1). Dry and crush the original soil to pass through a 2mm sieve to obtain dry soil powder with a particle size less than 2mm.

[0082] (2). Mix the dry soil powder obtained in step (1) 63%, polyvinyl alcohol fiber 0.0%, nano-silicon dioxide 2.2%, cement 9.0% and dispersant 0.2% by mass percentage and introduce into the blender to stir for 6-8 minutes until the mixture is uniform.

[0083] (3). Pour seawater (according to the mass content in Table 1 into the mixture in the blender, and continue to stir for 10-12 minutes until the mixture forms a uniform cement slurry.

[0084] (4). Pour the mixed cement slurry into a transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, keep the mold on the vibration table to vibrate until the mold is full and the bubbles are removed.

[0085] (5). Label the sample number and demold after 48 hours of curing at 20℃±2℃, and the target product is obtained.

[0086] Comparative Example 4

[0087] (1). Dry and crush the original soil to pass through a 2mm sieve to obtain dry soil powder with a particle size less than 2mm.

[0088] (2). Mix the dry soil powder obtained in step (1) 63%, polyvinyl alcohol fiber 0.0%, nano-silicon dioxide 0.0%, cement 9.0% and dispersant 0.2% by mass percentage and introduce into the blender to stir for 6-8 minutes until the mixture is uniform.

[0089] (3). Pour fresh water (according to the mass content in Table 1 into the mixture in the blender, and continue to stir for 10-12 minutes until the mixture forms a uniform cement slurry.

[0090] (4). The mixed cement paste is poured into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, the mold is placed on a vibration table to keep vibrating until the mold is full and the bubbles are removed.

[0091] (5). The sample number is marked, and after 48 hours of curing at 20°C ± 2°C, the mold is removed, and the target product is obtained.

[0092] Comparative Example 5

[0093] (1). The original soil is dried and crushed through a 2 mm sieve to obtain dry soil powder with a particle size less than 2 mm.

[0094] (2). The dry soil powder obtained in step (1) is mixed with polyvinyl alcohol fiber 1.2%, nano-silica 0.0%, cement 9.0%, and dispersant 0.2% according to the mass percentage, and introduced into a blender for stirring for 6-8 minutes until the mixture is uniform.

[0095] (3). The polyvinyl alcohol fiber needs to be dispersed by ultrasonic treatment before being added.

[0096] (4). Fresh water (according to the mass content in Table 1) is poured into the mixture in the blender, and continues to stir for 10-12 minutes until the mixture forms a uniform cement paste.

[0097] (5). The mixed cement paste is poured into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, the mold is placed on a vibration table to keep vibrating until the mold is full and the bubbles are removed.

[0098] (6). The sample number is marked, and after 48 hours of curing at 20°C ± 2°C, the mold is removed, and the target product is obtained.

[0099] Comparative Example 6

[0100] (1). The original soil is dried and crushed through a 2 mm sieve to obtain dry soil powder with a particle size less than 2 mm.

[0101] (2). The dry soil powder obtained in step (1) is mixed with polyvinyl alcohol fiber 0.0%, nano-silica 2.2%, cement 9.0%, and dispersant 0.2% according to the mass percentage, and introduced into a blender for stirring for 6-8 minutes until the mixture is uniform.

[0102] (3). Fresh water (according to the mass content in Table 1) is poured into the mixture in the blender, and continues to stir for 10-12 minutes until the mixture forms a uniform cement paste.

[0103] (4). The mixed cement paste is poured into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, the mold is placed on a vibration table to keep vibrating until the mold is full and the bubbles are removed.

[0104] (5). The sample number is marked, and after 48 hours of curing at 20°C ± 2°C, the mold is demolded to obtain the target product.

[0105] Comparative Example 7

[0106] (1). The original soil is dried and crushed through a 2mm sieve to obtain dry soil powder with a particle size of less than 2mm.

[0107] (2). The dry soil powder obtained in step (1) is mixed with polyvinyl alcohol fiber 1.2%, nano-silica 1.9%, cement 9.0% and dispersant 0.2% according to the mass percentage, and introduced into the blender for stirring for 6-8 minutes until the mixture is uniform.

[0108] (3). The polyvinyl alcohol fiber needs to be dispersed by ultrasonic treatment before being added.

[0109] (4). Fresh water (according to the mass content in Table 1, pour into the mixture in the blender, and continue to stir for 10-12 minutes until the mixture forms a uniform cement paste.

[0110] (5). The mixed cement paste is poured into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, the mold is placed on a vibration table to keep vibrating until the mold is full and the bubbles are removed.

[0111] (6). The sample number is marked, and after 48 hours of curing at 20°C ± 2°C, the mold is demolded to obtain the target product.

[0112] Comparative Example 8

[0113] (1). The original soil is dried and crushed through a 2mm sieve to obtain dry soil powder with a particle size of less than 2mm.

[0114] (2). The dry soil powder obtained in step (1) is mixed with polyvinyl alcohol fiber 2.0%, nano-silica 1.0%, cement 10.0% and dispersant 0.2% according to the mass percentage, and introduced into the blender for stirring for 6-8 minutes until the mixture is uniform.

[0115] (3). The polyvinyl alcohol fiber needs to be dispersed by ultrasonic treatment before being added.

[0116] (4). Sea water (according to the mass content in Table 1, pour into the mixture in the blender, and continue to stir for 10-12 minutes until the mixture forms a uniform cement paste.

[0117] (5). Pour the mixed cement paste into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, place the mold on a vibrating table and keep it vibrating until the mold is full and the bubbles are removed.

[0118] (6). Mark the sample number, and after 48 hours of curing at 20°C ± 2°C, demold to obtain the target product.

[0119] Comparative Example 9

[0120] (1). Dry and crush the retrieved undisturbed soil through a 2 mm sieve to obtain dry soil powder with a particle size less than 2 mm.

[0121] (2). Mix the dry soil powder obtained in step (1) 60%, polyvinyl alcohol fiber 0.5%, nano-silica 2.5%, cement 9.0%, and dispersant 0.2% by mass percentage, and introduce them into a blender and stir for 6-8 minutes until they are evenly mixed.

[0122] (3). The polyvinyl alcohol fiber needs to be dispersed by ultrasonic treatment before being added.

[0123] (4). Pour the seawater (according to the mass content in Table 1) into the mixture in the blender, and continue to stir for 10-12 minutes until the mixture forms a uniform cement paste.

[0124] (5). Pour the mixed cement paste into a cylindrical transparent plastic mold with a diameter of 39 mm and a height of 78 mm. During the pouring process, place the mold on a vibrating table and keep it vibrating until the mold is full and the bubbles are removed.

[0125] (6). Mark the sample number, and after 48 hours of curing at 20°C ± 2°C, demold to obtain the target product.

[0126] The cement-soil samples prepared in Examples 1-3 and Comparative Examples 1-9 were subjected to unconfined compressive strength tests, and the performance parameters are shown in Table 1:

[0127] Table 1 Performance parameter results of unconfined compressive strength of cement-soil samples of Examples 1-3 and Comparative Examples 1-9 after 28 days

[0128]

[0129] From the experimental results, it can be seen that the brittleness of cement soil can be significantly improved by adding polyvinyl alcohol fiber. The unconfined compressive strength of cement soil without adding nano-silica and polyvinyl alcohol fiber in Comparative Example 1 is 1.91 MPa, which causes brittle failure; the unconfined compressive strength of cement soil only mixed with 1.2% polyvinyl alcohol fiber in Comparative Example 2 is 2.55 MPa, which does not cause brittle failure, and the growth rate is 33.5% compared with Comparative Example 1; the unconfined compressive strength of cement soil only mixed with 2.2% nano-silica in Comparative Example 3 is 3.63 MPa, which causes brittle failure, and the growth rate is 90.1% compared with Comparative Example 1.

[0130] The unconfined compressive strength of cement soil mixed with 1.2% polyvinyl alcohol fiber and 1.9% nano-silica in Example 1 is 5.02 MPa, which does not cause brittle failure, and the growth rate is 162.8% compared with Comparative Example 1; the unconfined compressive strength of cement soil mixed with 0.8% polyvinyl alcohol fiber and 2.1% nano-silica in Example 2 is 5.09 MPa, which does not cause brittle failure, and the growth rate is 166.5% compared with Comparative Example 1; the unconfined compressive strength of cement soil mixed with 1.0% polyvinyl alcohol fiber and 2.2% nano-silica in Example 3 is 5.23 MPa, which does not cause brittle failure, and the growth rate is 173.8% compared with Comparative Example 1.

[0131] Comparative Examples 4-7 are comparative examples in which seawater is replaced with fresh water. The unconfined compressive strength of cement soil without adding nano-silica and polyvinyl alcohol fiber in Comparative Example 4 is 2.85 MPa, which causes brittle failure; the unconfined compressive strength of cement soil only mixed with 1.2% polyvinyl alcohol fiber in Comparative Example 5 is 3.71 MPa, which does not cause brittle failure, and the growth rate is 30.2% compared with Comparative Example 4; the unconfined compressive strength of cement soil only mixed with 2.2% nano-silica in Comparative Example 6 is 5.24 MPa, which causes brittle failure, and the growth rate is 83.9% compared with Comparative Example 4; the unconfined compressive strength of cement soil mixed with 1.2% polyvinyl alcohol fiber and 1.9% nano-silica in Comparative Example 7 is 6.36 MPa, which does not cause brittle failure, and the growth rate is 123.2% compared with Comparative Example 4.

[0132] Comparative Example 1 and Comparative Example 4 are both cement soil without adding nano-silica and polyvinyl alcohol fiber. The unconfined compressive strength of cement soil prepared by seawater in Comparative Example 1 is 1.91 MPa, which is 33% lower than the unconfined compressive strength of 2.85 MPa of cement soil prepared by fresh water in Comparative Example 4.

[0133] The unconfined compressive strength of the cement soil of Comparative Example 2 prepared from seawater is 2.55 MPa, which is 31.3% lower than the unconfined compressive strength of the cement soil of Comparative Example 5 prepared from fresh water, which is 3.71 MPa.

[0134] The unconfined compressive strength of the cement soil of Comparative Example 3 prepared from seawater is 3.63 MPa, which is 30.7% lower than the unconfined compressive strength of the cement soil of Comparative Example 6 prepared from fresh water, which is 5.24 MPa.

[0135] Comparative Examples 8 and 9 are not the composite cement soil prepared according to the optimal ratio, and the unconfined compressive strength is improved compared with Comparative Example 1, but there is a gap compared with Examples 1 to 3.

[0136] The optimal ratio of the fiber and nano-silica is determined by a large number of experiments in the present application, which avoids affecting the performance of the combined application of the fiber and nano-silica due to excessive or insufficient addition. When the amount of polyvinyl alcohol fiber is too much, the fiber is difficult to form effective bonding with the cement soil matrix due to insufficient hydration products, and the fiber is prone to agglomeration, thereby limiting the full play of the function of the fiber. Too little polyvinyl alcohol fiber will make it difficult to significantly improve the crack resistance of the composite cement soil. When the amount of nano-silica is too much, although the mechanical strength is improved, the increment is low, and the crack resistance of the composite cement soil is not significantly improved, and the application effect is limited. Too little nano-silica is difficult to generate enough hydration products to fill the defect pores of the cement soil, and the fiber and the cement soil matrix are difficult to form a firm mechanical chain, resulting in that the advantages of the combined application of the fiber and the nano-silica are not significant. The strength growth rate of the composite cement soil prepared by nano-silica and polyvinyl alcohol fiber can only exceed the sum of the growth rates of the fiber cement soil and the nano-cement soil, and only by using the optimal amount of materials determined in the present application and the corresponding preparation method, the best solidification effect can be achieved.

[0137] In the present application, the unconfined compressive strength of the composite cement soil prepared by seawater in Example 1 is 5.02 MPa, which is 21.0% lower than the unconfined compressive strength of 6.36 MPa of the composite cement soil prepared by freshwater in Comparative Example 7. However, freshwater resources are extremely scarce in remote coastal areas and island areas. Although the strength of freshwater is slightly higher, long-distance transportation of freshwater not only significantly increases the cost, but also increases energy consumption, and a temporary water supply system needs to be established, thereby further increasing the engineering cost. The experimental data show that the combined application of nano-silicon dioxide and polyvinyl alcohol fiber has the best effect, the unconfined compressive strength of the composite cement soil prepared by seawater is stronger than that of ordinary cement soil, the unconfined compressive strength of the composite cement soil prepared by seawater has the smallest decrease compared with that of the composite cement soil prepared by freshwater, and the unconfined compressive strength of the composite cement soil prepared by seawater in the present application is not much different from that of the composite cement soil prepared by freshwater. Therefore, compared with the preparation of composite cement soil by freshwater, the present application has significant economic benefits. In addition, the growth rate of the composite content is greater than the total of each single content growth rate, the synergistic effect of nano-silicon dioxide and polyvinyl alcohol fiber significantly enhances the mechanical properties, crack resistance and seawater corrosion resistance of the cement soil, and effectively inhibits the brittle failure of the cement soil, so that it can be stably applied in coastal soft soil foundation reinforcement engineering for a long time.

[0138] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A composite cement-soil formulated from seawater, nano-silica, and polyvinyl alcohol fiber, characterized in that, The raw materials of the composite cement-soil, by mass percentage, include: 63%–70% dry soil powder, 9%–10% silicate cement, 1.9%–2.2% nano-silica, 0.8%–1.2% polyvinyl alcohol fiber, 0.2% dispersant, and 16.6%–24.7% seawater; the nano-silica has a particle size of 20±5 nm and a specific surface area of ​​160–190 m² / g; the polyvinyl alcohol fiber has a length of 6±1 mm, an equivalent diameter of 16±1 µm, and a density of 1.29±0.1 g / cm³. 3 Before being added, polyvinyl alcohol fibers need to be dispersed using ultrasonic vibration screen technology; the mass ratio of sea salt to water in the seawater is (32-38):1000; the dispersant is polyvinylpyrrolidone K30; and the silicate cement is PO 42.5 silicate cement.

2. The composite cement-soil according to claim 1, characterized in that, The method for obtaining the dry soil powder is as follows: the collected soil sample at a depth of 15±1m is evenly spread out and placed outdoors for natural evaporation for 40-50 hours. After natural evaporation, the soil sample is crushed, placed in an oven at 105±5℃ and dried for 20-30 hours, then taken out and cooled, and passed through a 2 mm sieve to obtain dry soil powder.

3. The application of a composite cementitious soil prepared from seawater, nano-silica, and polyvinyl alcohol fiber as described in any one of claims 1-2, characterized in that, Used for the preparation of coastal transportation roadbeds and pile foundations in coastal and island / reef areas.

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