A method for in-situ modification and curing of lignin-based composite curing agents

Abstract

This invention relates to the field of engineering waste soil solidification and improvement, and particularly to a method for in-situ modification and solidification of lignin composite solidifying agent. The method includes: uniformly mixing the engineering waste soil to be solidified with cement; calculating the required amount of water to be added according to the optimum moisture content of the engineering waste soil; dissolving water glass and lime in water to generate amorphous calcium silicate, then dissolving sodium lignin sulfonate in the solution; finally, mixing the suspension containing lime, water glass, and sodium lignin sulfonate with the engineering waste soil uniformly; compacting the mixture to its maximum dry density; and curing for at least 7 days. The solidification of engineering construction waste soil using the technical solution of this application has the advantages of low cost, simple operation, high material efficiency, and no secondary pollution.

Description

Technical Field

[0001] This invention relates to the field of solidification and improvement of engineering waste soil, and particularly to the in-situ modification of lignin-based composite solidifying agents and their application in the field of improving low liquid limit silty clay engineering construction waste soil. Background Technology

[0002] Low-liquid-limit silty clay is characterized by low strength, poor water stability, and sensitivity to freeze-thaw cycles. Using low-liquid-limit silty clay as roadbed fill can easily cause moisture migration in the roadbed, resulting in frost heave in winter and frost heave in spring, which seriously affects the service performance of the roadbed. Therefore, when constructing highways in low-liquid-limit silty clay areas, in order to avoid the high cost of replacement and to follow my country's concept of sustainable development, the silty clay should be improved before use.

[0003] Lignin is a byproduct of the pulp and paper industry. Over 95% of lignin byproducts are discharged into rivers as "black liquor" or concentrated and incinerated, rarely being effectively utilized. However, lignin is a high-molecular-weight substance composed of several aromatic rings linked together, and its molecular structure contains active groups such as phenolic and alcoholic hydroxyl groups. Chemically modifying lignin to improve its reactivity and preparing green solidification agents for use in the solidification of low-liquid-limit silty clays reduces the consumption of chemical agents and their potential environmental damage. Furthermore, the introduction of lignin into the molecular structure enables biodegradation, making it an ideal way to turn waste into treasure. However, traditional methods involve chemically modifying lignin before using it to solidify slag. These methods suffer from low agent utilization efficiency, increased costs, and secondary pollution problems caused by wastewater and waste residue generated during the modification process.

[0004] This invention achieves the goal of treating waste with waste and reducing curing costs by integrating lignin modification and curing. Summary of the Invention

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The method for in-situ modification and curing of lignin composite curing agent disclosed in this invention includes the following steps:

[0007] Mix the construction waste soil that needs to be solidified with cement evenly. Calculate the required amount of water to be added according to the optimum moisture content of the construction waste soil. First, dissolve water glass and lime in water to generate amorphous calcium silicate, then dissolve sodium lignosulfonate in it. Finally, mix the suspension containing lime, water glass and sodium lignosulfonate evenly with the construction waste soil, compact it to the maximum dry density of the mixed improved soil, and cure it for no less than 7 days.

[0008] Preferably, the cement content is 5-7% of the dry weight of the construction waste that needs to be solidified.

[0009] Preferably, the mass ratio of sodium lignosulfonate to dry soil is 1:500-1000.

[0010] Preferably, the mass ratio of lime to dry soil is 1:300-1000.

[0011] Preferably, the mass ratio of lime to water glass is 1:1-6, wherein the modulus of the water glass is 3.3-4.2.

[0012] Ideally, the curing temperature should be 20–25°C, and the curing time should be at least 7 days.

[0013] Preferably, the moisture content of the mixed soil during mixing and compaction should be ±2% of the optimum moisture content, and the compaction density should be close to the maximum dry density.

[0014] Therefore, the present invention has the following beneficial effects:

[0015] (1) In this invention, lime and water glass are preferentially mixed and reacted to generate amorphous calcium silicate, which is then added to low liquid limit silty clay engineering slag for solidification. This process provides crystal nuclei for cement hydration, reduces the energy barrier for cement hydration, and thus promotes cement hydration. In addition, this scheme utilizes another product generated after the reaction of water glass and lime, sodium hydroxide, to hydroxylate lignin, improve the activity of lignin, and thus promote the purpose of lignin binding soil particles.

[0016] (2) This method uses low-activity lignin for the solidification of construction waste, which is of great significance for treating waste with waste, reducing solidification costs, and improving the resource value of construction waste.

[0017] (3) The preparation method of this scheme is simple to operate, the modification and curing are carried out at the same time, the material utilization rate is high, the time cost is saved, and no secondary pollution is generated.

[0018] (4) Compared with the traditional improvement method of lime and water glass, this scheme greatly reduces the amount of lime and water glass added, aiming to interact with lignin to modify lignin, thereby producing a synergistic effect of the three. Attached Figure Description

[0019] Figure 1 The drying shrinkage properties of cured soil using the lignin-based composite curing agent of the present invention are measured. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1

[0022] This embodiment provides a method for in-situ modification and curing of lignin-based composite curing agent. The method includes the following steps: dry mixing the engineering waste soil to be cured with cement, calculating the required amount of water to be added according to the optimum moisture content of the engineering waste soil, dissolving water glass and lime in water to generate amorphous calcium silicate, then dissolving sodium lignin sulfonate, and finally mixing the suspension containing amorphous calcium silicate with the engineering waste soil, compacting it to the maximum dry density of the mixed modified soil, and curing it for no less than 7 days.

[0023] Step S1: Add 7% of the dry weight of the construction waste soil to the cement and dry mix thoroughly. The chemical composition of the construction waste soil is shown in Table 1.

[0024]

[0025] Step S2: Calculate the required amount of water to be added based on the optimum moisture content when the engineering waste soil has the maximum dry density. Dissolve lime and water glass in water. The mass ratio of lime to dry soil is 0.1% to 0.3%, and the mass ratio of lime to water glass is 1:1-6. The modulus of water glass is 3.7.

[0026] Step S3: Add sodium lignosulfonate to the suspension, with the mass ratio of sodium lignosulfonate to dry soil being 0.1% to 0.2%.

[0027] Step S4: After stirring, the suspension containing lime, water glass and sodium lignosulfonate is added to the engineering waste soil mixed with cement.

[0028] Step S5: Cure at a temperature of 20-25℃ for 7 days.

[0029] Control group 1: Construction waste soil was cured for 7 days under the same conditions as above after maintaining the optimal moisture content, mixing and compacting.

[0030] Control group 2 (cement): 7% cement was added to the construction waste soil by external admixture method. After mixing and compaction while maintaining the optimal moisture content, it was cured for 7 days under the same conditions as above.

[0031] Control group 3 (cement and lime): 7% cement and 0.2% lime were added to the construction waste soil. After mixing and compacting while maintaining the optimal moisture content, the mixture was cured for 7 days under the same conditions as above.

[0032] Control group 4 (cement sodium silicate): 7% cement and 0.4% sodium silicate were added to the construction waste soil. After mixing and compacting while maintaining the optimal moisture content, the mixture was cured for 7 days under the same conditions as above.

[0033] Table 2 shows the unconfined compressive strength results (7-day strength) of the solidified soil in Example 1.

[0034]

[0035] Table 3 Soil cohesion and internal friction angle

[0036]

[0037]

[0038] Experimental results show that the unconfined compressive strength, cohesion, internal friction angle and drying shrinkage deformation performance of the solidified soil in the examples of the present invention are all better than those of the control group 1-4.

Claims

1. A method for in-situ modification and curing of a lignin composite curing agent, characterized in that, The method includes the following steps: The construction waste soil that needs to be solidified is dry-mixed evenly with cement. The required amount of water to be added is calculated according to the optimum moisture content of the construction waste soil. Water glass and lime are first dissolved in water to generate amorphous calcium silicate and sodium hydroxide, and then sodium lignosulfonate is dissolved in them. The mass ratio of lime to water glass is 1:1-6, and the modulus of water glass is 3.3-4.

2. Finally, the suspension containing lime, water glass and sodium lignosulfonate is mixed evenly with the construction waste soil to form improved soil. The improved soil is compacted to its maximum dry density and cured for no less than 7 days.

2. The method for in-situ modification and curing of lignin composite curing agent according to claim 1, characterized in that, The modulus of the water glass is 3.

7.

3. The method for in-situ modification and curing of lignin composite curing agent according to claim 1, characterized in that, The mass ratio of sodium lignosulfonate to dry construction waste is 1:500-1000.

4. The method for in-situ modification and curing of a lignin composite curing agent according to claim 1, characterized in that, The mass ratio of lime to dry construction waste is 1:300-1000.

5. The method for in-situ modification and curing of a lignin composite curing agent according to claim 1, characterized in that, The moisture content of the mixed soil during mixing and compaction should be ±2% of the optimum moisture content, the curing temperature should be 20~25℃, and the curing time should be at least 7 days.

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