Preparation and use method of straw-based soft soil curing agent

Abstract

The invention relates to a preparation and use method of a soft soil curing agent, in particular to a preparation and use method of a straw-based soft soil curing agent. The technical problems that an existing soft soil curing agent is low in strength and poor in stability are solved. The method comprises the following steps: crushing straw, immersing the crushed straw into a NaOH solution, stirring, and filtering to obtain filtrate and a solid-phase substance; uniformly stirring the filtrate, water glass and laccase, and adjusting the pH value to 8-10 to obtain a composite exciting agent which is marked as a component A; performing high-temperature pyrolysis on the solid-phase substance to obtain porous hard carbon powder, and uniformly mixing the porous hard carbon powder with slag, fly ash and glass powder to obtain a mixed cementing material marked as a component B; the component A and the component B are combined to form the soft soil curing agent. The curing agent is added into to-be-cured soft soil, the mixture is uniformly mixed and cured, after curing, the cohesive force reaches 95 KPa or above, the internal friction angle tan alpha reaches 0.02951 and is 1.46 times and 7 times that of the cured soft soil with cement as the curing agent, and the curing agent can be used in soil engineering.

Description

Technical Field

[0001] The invention relates to a preparation method of a soft soil solidifying agent. Background Art

[0002] Coastal soft soil has the characteristics of high water content and large porosity. At the same time, it is corroded by the dry-wet cycle of seawater, making this type of high-porosity and easily corroded soft soil impossible to use in soil engineering. In order to improve this type of soft soil, a large amount of cement is often used to harden the soft soil to meet engineering requirements. Slag, fly ash and other industrial wastes are also added to the cement to reduce the amount of cement. However, it is difficult to completely fill the pores of the soil body with cementitious materials that rely solely on the hydration of cementitious cement, and the cement-based materials still have poor resistance to seawater erosion. In recent years, alkali-activated geopolymer concrete used in the construction industry is a solution. Alkali-activated geopolymer concrete relies on solid wastes such as slag, fly ash, and silica fume, and is formed by activating and curing them with alkaline activators. This type of concrete has good resistance to seawater erosion, but the mechanical strength of the soil is poor.

[0003] The Chinese patent application number 202010920486.6 discloses a soil curing agent, which is a method for preparing a soft soil curing agent using calcined solid waste materials, sodium metasilicate, lignin, sodium naphthalenesulfonate formaldehyde condensate, polyacrylamide, and hydroxymethyl cellulose. The method uses lignin and the material to be reacted to generate lignin sulfonate to achieve the purpose of curing soft soil. The strength of the cured material is higher than 2MPa, but the preparation process of the soil curing agent is relatively complicated, and polymerization reaction cannot occur inside the soil, and the effect of synergistic improvement of the compressive strength and shear strength of the soil cannot be achieved. The article "The Effect and Mechanism of In-situ Polymerization on the Mechanical Properties of 3D Printing Mortar" on pages 1093-1103 of Volume 5, Issue 51 of the Journal of the Chinese Ceramic Society in 2023 discloses the use of acrylamide as a monomer, potassium persulfate as an initiator, and N,N,-methylenebisacrylamide as a cross-linking agent to achieve in-situ polymerization in mortar. This study achieved in-situ polymerization inside the mortar, promoted the uniform distribution of monomer molecules in the gelling system, formed a continuous network structure and filled the pores, improved the density of the matrix, and effectively improved the mechanical properties of the 3D printed mortar. However, this solution requires N,N,-methylenebisacrylamide as a cross-linking agent to achieve in-situ polymerization, and cannot achieve the polymerization reaction of polymer monomers only under the action of the initiator. Moreover, as the curing age increases, the generated network structure will be wrapped by the hydration product, and cannot reflect the role of its network structure in the later stage of curing. Summary of the invention

[0004] The invention aims to solve the technical problems of low strength and poor stability of the existing soft soil solidifying agent, and provides a preparation and use method of a straw-based soft soil solidifying agent.

[0005] The preparation method of the straw-based soft soil solidifying agent of the present invention is carried out according to the following steps: 1. Weigh 25-35 parts of slag, 13-18 parts of fly ash, 13-18 parts of glass powder, 10 parts of corn stalks, 8-12 parts of 1%-3% NaOH solution, 13-18 parts of water glass, and 4-8 parts of laccase according to the weight ratio; 2. Use a BX-213 chipper to crush the straw weighed in step 1, and sieve it with an industrial standard sieve with a pore size of 0.2 mm, and take the bottom of the sieve to obtain straw powder; 3. Immerse the straw powder in a NaOH solution weighed in step 1 at a temperature of 90-95°C and a mass percentage concentration of 1%-3%, and stir for 15-30 minutes, then filter to obtain a filtrate and a solid phase; in this step, soaking with alkali can separate the cellulose and lignin in the straw, and the filtrate contains lignin, hemicellulose and a small amount of cellulose, and the solid phase is cellulose; 4. After the filtrate obtained in step 3 is uniformly stirred with the water glass and laccase weighed in step 1, the pH value is adjusted to 8-10 to obtain a composite activator, which is recorded as component A; 5. Put the solid phase obtained in step 3 into a high temperature furnace, heat it to 600-800°C at a heating rate of 5°C / min and keep it for 3-5 hours for high temperature pyrolysis, cool it to room temperature and grind it through a 200 mesh sieve to obtain a porous hard carbon powder; 6. The porous hard carbon powder prepared in step 5, the slag, fly ash and glass powder weighed in step 1 are mixed evenly to obtain a mixed cementitious material, which is recorded as component B; the combination of component A and component B is called a straw-based soft soil solidifier.

[0006] Furthermore, the straw in step 1 is wheat, rice, corn, potato, rapeseed, cotton or sugarcane straw.

[0007] Furthermore, in step 1, 30 parts of slag, 15 parts of fly ash, 15 parts of glass powder, 10 parts of corn stalks, 10 parts of NaOH solution with a mass percentage concentration of 1% to 3%, 15 parts of water glass, and 5 parts of laccase were weighed in proportion by weight. Furthermore, the laccase in step six is ​​a bacterial laccase derived from bacteria.

[0008] The method for solidifying soft soil using the straw-based soft soil solidifying agent is carried out according to the following steps: Add the straw-based soft soil solidifier to the soft soil to be solidified and mix evenly. Curing is carried out for 24 to 30 days at a temperature of 20 to 30°C and a relative humidity of 90 to 95% to complete the solidification of the soft soil.

[0009] The straw left after harvesting wheat, rice, corn, potatoes, rapeseed, cotton, sugarcane and other crops contains a large amount of nitrogen, phosphorus, potassium, calcium, magnesium, organic matter, cellulose and lignin, which is a renewable biological resource. The cellulose in the straw is separated from the lignin by NaOH solution, and the lignin is dissolved in the NaOH solution. The filtrate and cellulose containing lignin, hemicellulose and a small amount of cellulose are obtained by filtration. After the filtrate is mixed with water glass, a composite activator is obtained; the cellulose is pyrolyzed at high temperature. At 200°C, the cellulose will first decompose into soluble oligosaccharides, and the oligosaccharides will be further hydrolyzed into glucose monomers. These monomers are dehydrated and cracked to produce intermediate products such as 5-hydroxymethylfurfural and its derivatives. These intermediate products undergo polymerization, condensation and other reactions to finally produce biochar. As the temperature rises to 600°C, the functional groups in the biochar undergo decarboxylation and decarbonization reactions, resulting in an increase in the aromaticity of the biochar, thereby increasing the reactivity of the biochar and producing gaseous products such as methane. The biochar obtained by pyrolysis is cooled to room temperature and then ground through a 200-mesh sieve to obtain biochar powder, which further improves the reaction activity of the biochar powder. At the same time, the generated methane gas can be used in natural gas production.

[0010] Lignin is a complex phenolic polymer formed by three alcohol monomers (p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol). Laccase is a glycoprotein belonging to the blue copper family of polyphenol oxidases. After adding the curing agent cementitious material, biochar powder, laccase and composite activator to the soil, during the hydration of the cementitious material, laccase can directly catalyze the oxidation of lignin dissolved in the NaOH solution into phenoxy active free radical intermediates. These active free radical intermediates can spontaneously couple through CC, CN, and CO to generate a variety of dimer isomers. At the same time, since the dimer still retains the phenolic hydroxyl functional group, it can be oxidized by laccase again to form phenoxy active free radical intermediates. These free radical intermediates are further oxidized with phenolic substrates to form complex trimers, tetramers and polymers, etc., to achieve the in vitro polymerization reaction of lignin. In this patent, a composite activator is obtained by adding water glass to a mother liquor containing lignin, and then adding it to soft soil together with laccase, so that a polymerization reaction occurs inside the soft soil to form a uniform polymer network, thereby improving the compressive strength of the soil and the shear strength of the soil. At the same time, the porous biochar powder fills the pores of the soil, improves the density of the soil, enhances the ability of the solidified soil to resist seawater erosion, and also improves the mechanical properties of the soil.

[0011] The present invention separates straw into lignin and cellulose and mixes them into soft soil, which can also reduce the use of cement, reduce carbon emissions, and improve the mechanical properties and durability of the soil. The cohesion of the soft soil solidified by the soft soil solidifying agent of the present invention reaches more than 95KPa, which is 1.46 times that of the solidified soft soil with cement as the solidifying agent. At the same time, the internal friction angle (tanα) of the solidified soft soil reaches 0.02951, which is 7 times that of the solidified soft soil with cement as the solidifying agent. The present invention realizes the high-value utilization of agricultural waste and the recycling process is simple, and can be used in soil engineering. DETAILED DESCRIPTION

[0012] The beneficial effects of the present invention are verified by the following examples.

[0013] Example 1: The preparation method of the straw-based soft soil solidifying agent of this example is carried out according to the following steps: 1. According to weight, weigh 30 parts of slag, 15 parts of fly ash, 15 parts of glass powder, 10 parts of corn stalks, 10 parts of 1% NaOH solution, 15 parts of water glass, and 5 parts of laccase; the laccase is a bacterial-derived alkaline bacterial laccase purchased from Sigma-Aldrich, the product name is laccase (derived from Versicolor versicolor), model: 38429, it is a light brown powder, and the purity is> 0.5 U / mg; 2. Use a BX-213 chipper to crush the corn stalks weighed in step 1, and sieve them with an industrial standard sieve with a pore size of 0.2 mm, and take the bottom of the sieve to obtain stalk powder; 3. Immerse the straw powder in the NaOH solution weighed in step 1 at a temperature of 95°C and a mass percentage concentration of 1%, stir for 0.5 hours, and then filter to obtain a filtrate and a solid phase; the alkali soaking in this step can separate the cellulose and lignin in the straw, and the filtrate contains lignin, hemicellulose and a small amount of cellulose, and the solid phase is cellulose; 4. After the filtrate obtained in step 3 is uniformly stirred with the water glass and laccase weighed in step 1, the pH value is adjusted to 9 to obtain a composite activator, which is recorded as component A; 5. Put the solid phase obtained in step 3 into a high temperature furnace, heat it to 600°C at a heating rate of 5°C / min and keep it for 4 hours for high temperature pyrolysis, cool it to room temperature and grind it through a 200 mesh sieve to obtain porous hard carbon powder; 6. The porous hard carbon powder prepared in step 5, the slag, fly ash and glass powder weighed in step 1 are mixed evenly to obtain a mixed cementitious material, which is recorded as component B; the combination of component A and component B is called a straw-based soft soil solidifier.

[0014] Comparative Example 1: The preparation method of the soft soil solidifying agent in this comparative example is: weigh 60 parts of slag, 5 parts of NaOH aqueous solution with a mass percentage concentration of 1% and 5 parts of water glass by weight; mix the NaOH aqueous solution and the water glass evenly, recorded as component A; the slag is recorded as component B; the combination of component A and component B is called a soft soil solidifying agent.

[0015] Comparative Example 2: The preparation method of the soft soil solidifying agent in this comparative example is: weigh 40 parts of slag, 20 parts of fly ash, 5 parts of 1% NaOH aqueous solution and 5 parts of water glass by weight; mix the NaOH aqueous solution and the water glass evenly, recorded as component A; mix the slag and the fly ash evenly, recorded as component B; the combination of component A and component B is called a soft soil solidifying agent.

[0016] Comparative Example 3: The preparation method of the soft soil solidifying agent in this comparative example is: weigh 30 parts of slag, 15 parts of fly ash, 15 parts of glass powder, 5 parts of 1% NaOH aqueous solution and 5 parts of water glass by weight; mix the NaOH aqueous solution and the water glass evenly, recorded as component A; mix the slag, fly ash and glass powder evenly, recorded as component B; the combination of component A and component B is called a soft soil solidifying agent.

[0017] Comparative Example 4: The soft soil solidifying agent in this comparative example is cement.

[0018] The straw-based soft soil curing agent prepared in Example 1 and the soft soil curing agents of Comparative Examples 1 to 4 were simultaneously subjected to a soft soil curing test. A soft soil with a natural moisture content of 40% in a coastal area of ​​South China was used as the test soft soil. The soft soil curing agent and the soft soil curing agent were added to the soft soil to be cured and mixed evenly, wherein the soft soil curing agent accounted for 20% of the mass of the mixture, and then covered with a plastic film. After curing for 28 days at a temperature of 20° C. and a relative humidity of 95%, the cohesion and internal friction angle of the cured soft soil were tested, and the results are shown in Table 1.

[0019] Table 1 Experimental results of soft soil solidifier

[0020] The cohesion of the cured soft soil prepared with the soft soil curing agent of Example 1 is higher than that of the cured soft soil prepared with the soft soil curing agent of other comparative examples, and is 1.46 times that of the cured soft soil with cement as the curing agent. At the same time, the internal friction angle of the cured soft soil prepared with the soft soil curing agent of Example 1 is higher than that of the cured soft soil prepared with the soft soil curing agent of other comparative examples, and is 7 times that of the cured soft soil with cement as the curing agent.

[0021] In Example 1, the cellulose in the straw is pyrolyzed at 600°C to form porous hard carbon powder, and the porous hard carbon powder is ground through a 200-mesh sieve and added to the soil. After grinding, the porous hard carbon powder can activate the activity of biochar, and at the same time, the porous hard carbon powder can play a certain adsorption role in the soil, which can improve the density of the soil to a certain extent, and can improve the mechanical properties and durability of the soil. The composite stimulant prepared from straw in Example 1 contains ions such as phosphorus, potassium, and calcium. These alkali metal ions have a certain enhancing and stimulating effect on geopolymer concrete. For example, calcium ions can enhance the CSH and CASH gels in geopolymer concrete. At the same time, during the hydration process of the cementitious material, the lignin in the composite stimulant undergoes a polymerization reaction synchronously inside the soil under the action of laccase to form a uniform high molecular polymer network, which improves the compressive strength of the soil while improving the shear strength of the soil.

[0022] The present invention extracts cellulose and lignin from the straw for solidifying soft soil, which is beneficial to solving the problem of excessive carbon emissions in the construction industry and can reduce environmental pollution. It is green and environmentally friendly, has good economic benefits, and improves resource utilization.

Claims

1. A method for preparing a straw-based soft soil solidifying agent, characterized in that The method proceeds as follows:

1. Weigh 25-35 parts of slag, 13-18 parts of fly ash, 13-18 parts of glass powder, 10 parts of corn stalks, 8-12 parts of 1%-3% NaOH solution, 13-18 parts of water glass, and 4-8 parts of laccase according to the weight ratio; 2. Use a BX-213 chipper to crush the corn stalks weighed in step 1, and sieve them with an industrial standard sieve with a pore size of 0.2 mm, and take the bottom of the sieve to obtain stalk powder; 3. Immerse the straw powder in a NaOH solution weighed in step 1 at a temperature of 90-95°C and a mass percentage concentration of 1%-3%, and stir for 15-30 minutes, then filter to obtain a filtrate and a solid phase; in this step, soaking with alkali can separate the cellulose and lignin in the straw, and the filtrate contains lignin, hemicellulose and a small amount of cellulose, and the solid phase is cellulose; 4. After the filtrate obtained in step 3 is uniformly stirred with the water glass and laccase weighed in step 1, the pH value is adjusted to 8-10 to obtain a composite activator, which is recorded as component A; 5. Put the solid phase obtained in step 3 into a high temperature furnace, heat it to 600-800°C at a heating rate of 5°C / min and keep it for 3-5 hours for high temperature pyrolysis, cool it to room temperature and grind it through a 200 mesh sieve to obtain a porous hard carbon powder; 6. The porous hard carbon powder prepared in step 5, the slag, fly ash and glass powder weighed in step 1 are mixed evenly to obtain a mixed cementitious material, which is recorded as component B; the combination of component A and component B is called a straw-based soft soil solidifier.

2. The method for preparing a straw-based soft soil solidifying agent according to claim 1, characterized in that: The straw described in step 1 is wheat, rice, corn, potato, rape, cotton or sugarcane straw.

3. The method for preparing a straw-based soft soil solidifying agent according to claim 1 or 2, characterized in that: In step 1, 30 parts of slag, 15 parts of fly ash, 15 parts of glass powder, 10 parts of corn stalks, 10 parts of NaOH solution with a mass percentage concentration of 1% to 3%, 15 parts of water glass, and 5 parts of laccase are weighed according to the weight ratio.

4. The method for preparing a straw-based soft soil solidifying agent according to claim 1 or 2, characterized in that: The laccase described in step six is ​​a bacterial laccase derived from bacteria.

5. A method for using a straw-based soft soil solidifying agent prepared by the method of claim 1 for soft soil solidification, characterized in that: The method is carried out according to the following steps: adding a straw-based soft soil curing agent to the soft soil to be cured and mixing evenly, curing for 24 to 30 days under the conditions of a temperature of 20 to 30°C and a relative humidity of 90% to 95%, and completing the curing of the soft soil.

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