Water stable anti-deformation curing agent for swelling soil and method of use thereof

Abstract

The present application relates to the field of soil stabilizer, especially to the water stable anti-deformation stabilizer suitable for swelling soil and its using method. In the present application, two components of cationic polyacrylamide and sepiolite powder are used in the cement-based stabilizer, the water in the system is fixed by the two components, the water entering into the interlayer of the montmorillonite system in the swelling soil is reduced, and the dry-wet resistance and water stability of the system are obviously improved.

Description

Technical Field

[0001] This application relates to the field of soil stabilizers, and in particular to water-stable, deformation-resistant stabilizers suitable for expansive soils and their application methods. Background Technology

[0002] Expansive soil is a hydrophilic clay mineral mainly composed of montmorillonite and illite. The montmorillonite it contains has a layered structure. In a humid environment, the interlayers of montmorillonite can absorb a large amount of water, causing the interlayer spacing to increase and the soil volume to expand. However, during dehydration, the interlayers lose water and the interlayer spacing shrinks, leading to soil shrinkage and cracking. This also brings trouble to the solidification process of expansive soil.

[0003] Soil stabilizers are civil engineering materials used to solidify loose soil. Inorganic stabilizers, in particular, are those that use hydration reactions with cement to generate gel-like substances that bind the soil. They are inexpensive, widely available, and can incorporate various inorganic solid wastes (such as tailings, metal slag, volcanic ash, quicklime, and fly ash), thus having wide applications. However, the use of inorganic stabilizers in expansive soils typically presents significant drawbacks. Firstly, for interlayered structures like montmorillonite, the gel system struggles to penetrate the interlayers, making it difficult to fix the soil layers and leading to increased slippage between layers, resulting in a loose structure and reduced strength. Secondly, cement systems have weak resistance to drying shrinkage, making expansive soils prone to cracking and breakage under varying humidity levels, even after solidification, further reducing their strength. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a curing agent based on inorganic components such as cement, which can achieve better penetration and curing effects in moist expansive soil systems, reducing cracking after drying.

[0005] First, this application provides a water-stabilized, deformation-resistant curing agent suitable for expansive soil, comprising the following components by weight: 70 parts cement 15-30 parts of calcium-based activator 10-20 parts fly ash 5-10 parts sepiolite powder 10-20 parts of lithium slag 3-6 parts of water-reducing agent 1-3 parts of cationic polyacrylamide; The calcium-based activator is quicklime, gypsum, or a combination of both.

[0006] Overall, the above scheme employs a cement-based strength framework structure, forming CSH gel through hydration reaction to provide the basic strength system. Building upon this basic strength system, this application first utilizes a calcium-based activator. This activator provides a large number of calcium ions, replacing sodium and potassium ions on the surface of the expansive soil, reducing the interlayer spacing of the montmorillonite structure and mitigating its potential for wet expansion and shrinkage. Simultaneously, fly ash is added to the system. Under the action of this activator, the fly ash reacts with cement hydration to form an additional CSH and CAH gel system. Its finer particles can better fill the pores of the system, improving overall density. Lithium slag provides higher reactivity, replacing fly ash in the system and undergoing secondary hydration. Therefore, the overall system is more stable during curing, suppressing cracking during the curing process.

[0007] Based on the above, this application further adds sepiolite powder and cationic polyacrylamide. These two components are mainly added to address the problem of loose interlayer structure and easy slippage and cracking caused by the high water absorption of the expansive soil system. Sepiolite provides a large specific surface area and can provide better water absorption performance. During the curing process or in the cured soil, when the system is in a humid environment and absorbs a lot of water, sepiolite can provide better water absorption performance to reduce the accumulation of water between montmorillonite layers, thereby inhibiting the slippage between the layers caused by water absorption in the system under high humidity environment. It has a significant improvement on the overall strength and wet expansion and drying shrinkage. Cationic polyacrylamide can form organic bridging in the system and has a certain flocculation effect. Excessive addition will significantly reduce the fluidity of the system and make construction difficult. However, when added in small amounts, it can reduce the surface energy of bentonite, thereby reducing the water absorption of bentonite. At the same time, it can also improve the bonding performance between cement particles and soil particles in the soil, and improve the impermeability of the cured system. It should be noted that cationic polyacrylamide has a better flocculation effect in the system. It can be embedded into the montmorillonite interlayer through positively charged groups, which can better improve the overall water resistance. At the same time, its positively charged groups also have good adsorption on the surface of cement particles, which can play a better anchoring role.

[0008] Preferably, the sepiolite powder is pretreated using the following steps: Sepiolite powder is impregnated in an aqueous solution or a mixture of water and alcohol containing calcium ions, causing calcium ion exchange.

[0009] In the above scheme, the sepiolite powder undergoes preliminary treatment. After calcium ion loading, the sepiolite surface exhibits a higher affinity with the cement hydration system, thereby enhancing its affinity within the system and forming a stronger bond structure with the cement hydration products. Simultaneously, the loaded calcium ions can slowly participate in the system's hydration reaction during long-term curing. Even as the calcium ion concentration decreases in the later stages, it can provide continued reinforcement and significantly inhibit cracking during the preparation process. Furthermore, calcium ion exchange helps the sepiolite better form a filling effect and significantly reduces the system's drying shrinkage.

[0010] Preferably, the impregnation process of sepiolite powder is as follows: first, prepare an acidic solution with a pH of 2.5 to 4.5, add sepiolite to the solution for the first impregnation, and then add calcium ions to the system for the second impregnation.

[0011] In the above scheme, the method of first acid leaching and then calcium exchange is adopted. Compared with direct calcium ion exchange impregnation, the above scheme can utilize hydrogen ions to dissolve some magnesium and aluminum ions first to form a cavity structure. On the one hand, it helps calcium ions to enter the system better, and on the other hand, it helps the silicon active sites on the surface to be more fully exposed, so that the sepiolite powder can participate better in the subsequent hydration reaction.

[0012] It should be noted that in the above method, if the acid and calcium source are added simultaneously, a large amount of H+ will appear in the solution. + Will with Ca 2+ Competition for adsorption sites on the sepiolite surface leads to Ca... 2+ The modification effect on the system was significantly weakened, but in this scheme, acidification was performed first, followed by the addition of calcium ions, which significantly improved the ion exchange effect of calcium ions.

[0013] Further preferred, calcium hydroxide is used when adding calcium ions to the system.

[0014] In the above scheme, calcium hydroxide, as a calcium source, does not introduce additional chloride ions, thus reducing the potential corrosion risk of the system and having no significant adverse effect on the hydration reaction steps of the curing agent system. On the other hand, calcium hydroxide can adjust the pH value of the system, so there is no need to adjust the acidic conditions when adding the calcium source, which significantly improves the processing convenience of the system.

[0015] More preferably, when the sepiolite is impregnated in the acid solution, the solid-liquid ratio of the sepiolite to the acid solution is 5-10 g:100 mL, and / or, The acid immersion temperature is 50–80℃, the time is 5–10 min, and / or, The mass of the calcium hydroxide is 0.1 to 0.2 times the mass of the sepiolite, and / or, After the calcium hydroxide is added, the soaking time continues for 2 to 4 hours.

[0016] In the above scheme, the sepiolite can be fully dispersed in the liquid phase, while avoiding the difficulty of stirring the system due to excessive viscosity. Furthermore, calcium ions can effectively modify the sepiolite, further improving its surface activity, while preventing the system's interfacial activity from decreasing due to calcium ions completely occupying the surface. Simultaneously, the aforementioned time facilitates the full diffusion of calcium ions into the pores of the sepiolite, significantly improving the stability and water-wash resistance of the final system.

[0017] Preferably, the sepiolite powder is calcined before impregnation, with the calcination temperature being 300–500°C and the calcination time being 30–120 min.

[0018] The calcination process can remove the naturally adsorbed water from sepiolite and improve the capacity of the pores. It can also improve the dispersibility of the system and remove residual organic impurities. The final product has significantly improved strength. After the pores are modified, they can better participate in the cement hydration system, which significantly improves the overall strength.

[0019] Preferably, the gypsum is calcined gypsum, and the gypsum accounts for 10-30% of the mass of the calcium-based activator.

[0020] In the above scheme, calcined gypsum is selected because of its better solubility. It can participate in the ettringite system in the early stages and begin to compensate for shrinkage during the plastic stage of the slurry, thus avoiding cracking in the later stages. Meanwhile, in the above system, the mass ratio of gypsum to quicklime is controlled at 0.1–0.4:1 (where the mass of gypsum is calculated based on calcium sulfate, excluding its water of crystallization). Gypsum can provide appropriate expansion during the preparation process to compensate for the drying shrinkage of the cement and quicklime system, achieving system stability. Furthermore, it can control the overall setting time more stably, significantly improving the final strength.

[0021] Preferably, it also contains 5 to 10 parts by weight of silica fume.

[0022] In the above system, silica fume has a smaller average particle size, which can better fill the pores between cement particles and montmorillonite systems in expansive soil compared to cement particles and fly ash. It can achieve rapid reaction in the gaps of the above system by utilizing the high reactivity of its amorphous silica, thereby improving the density of the system and the bonding strength of the interface area. At the same time, it can also be combined with water-reducing agents to improve the flow properties of the system and reduce bleeding and segregation during the curing agent construction process.

[0023] Preferably, it further comprises 5 to 10 parts by weight of reinforcing short fibers, wherein the length distribution of the reinforcing short fibers is 3 to 6 mm.

[0024] In the above system, reinforcing short fibers can further improve crack resistance. During construction, short fibers can penetrate into the surface or part of the expansive soil, allowing the cracking performance during drying to be compensated by the bridging properties of the fibers. This significantly improves the impact toughness after curing. At the same time, it can also form a complementary structure with sepiolite powder. Sepiolite powder provides a thickening effect in the microscopic system, while reinforcing fibers provide mechanical support in the macroscopic system. The two work together to better improve the crack resistance of the curing agent during the modification of expansive soil by changes in wet and dry conditions.

[0025] In addition, this application also provides a method for using the above-mentioned water-stable anti-deformation curing agent. After mixing the components except cationic polyacrylamide and water-reducing agent, water and water-reducing agent are added to adjust the flowability of the grout at 25°C to 120-200 mm. Then, cationic polyacrylamide is added and sprayed, grouted, or directly mixed with the soil before curing is completed.

[0026] In the above scheme, the fluidity of the grout is controlled at 120-200mm. It can be applied by spraying, or by atmospheric pressure grouting, high pressure grouting and other processes. It can also be applied by pre-mixing with soil and then backfilling. The overall construction is simple, the spray does not flow on the slope, and the final strength is high after curing.

[0027] In summary, this application employs cationic polyacrylamide and sepiolite powder as components in the cement-based curing agent. These two components immobilize water in the system, reducing water ingress into the montmorillonite interlayer within the expansive soil, thereby significantly improving the system's resistance to wet and dry conditions and its water stability. Furthermore, the modification of sepiolite with calcium ions further enhances the mechanical strength of the curing agent during the soil curing process. Detailed Implementation

[0028] The technical solutions in this application will be further illustrated by the following specific embodiments.

[0029] In this application, the raw material components are selected as follows: Cement: Ordinary Portland 42.5 cement; Quicklime: Commercially available industrial calcium oxide; Fly ash: Commercially available Grade II fly ash; Lithium slag: Sourced from a lithium extraction plant, lithium slag extracted from lepidolite, and ground to 200 mesh; Silica fume: Silica content > 90%, specific surface area > 20m² 2 / g; Reinforced short fibers: PP short-cut fibers, average length 5mm; Cationic polyacrylamide: weight average molecular weight 10,000 ± 2,000,000, degree of ionization 25 ± 2%; Anionic polyacrylamide: weight-average molecular weight 10,000 ± 2,000,000, degree of ionization 25 ± 2%; Water-reducing agent: Commercially available polycarboxylate water-reducing agent (anti-mud type, solid content 20%); Sepiolite powder: raw sepiolite ore, crushed to 100 mesh.

[0030] First, the following preparation example is designed to modify sepiolite powder.

[0031] Preparation Example 1: Sepiolite was processed using the following steps: S1. Sepiolite powder was calcined at 400℃ for 50 min and then naturally cooled to room temperature. S2. Take deionized water, add hydrochloric acid, and adjust the pH to 3.0. Add the calcined sepiolite powder to the above system at a solid-liquid ratio of 10g / 100mL. Stir at 200rpm for 10min at 80℃. Then add calcium hydroxide to the above system at 0.1 times the mass of the sepiolite powder. Continue stirring for 2h. Then centrifuge and wash the filter cake three times with deionized water.

[0032] Preparation Example 2 differs from Preparation Example 1 in that, in step S2, the parameters are adjusted as follows: S2. Take deionized water, add hydrochloric acid, and adjust the pH to 3.0. Add the calcined sepiolite powder to the above system at a solid-liquid ratio of 5g / 100mL. Stir at 200rpm for 5min at 50℃. Then add calcium hydroxide to the above system at 0.2 times the mass of the sepiolite powder and continue stirring for 4h. Then centrifuge and wash the filter cake three times with deionized water until no chloride ions are detected by silver nitrate solution.

[0033] Preparation Example 3 differs from Preparation Example 1 in that the sepiolite powder is not calcined and is directly subjected to step S2.

[0034] Preparation Example 4 differs from Preparation Example 1 in that, in step S2, the process is performed directly with calcium hydroxide instead of acid impregnation.

[0035] Preparation Example 5 differs from Preparation Example 1 in that, in step S2, calcium chloride is used instead of calcium hydroxide, making the overall environment acidic during the calcium ion exchange process.

[0036] Based on the above preparation example, the following embodiments were further designed.

[0037] The following experiments were designed to verify the following embodiments: Take an expansive soil sample (moisture content 50±5%), mix the above-mentioned curing agent with the soil at a ratio of 1:10 (based on dry matter), backfill into the mold, compact it, and then cure it in an environment of 20℃ and 100%RH for 7 days, and then cure it in an environment of 20℃ and 60%RH for 21 days to obtain a sample for experiment.

[0038] 1. Refer to Section 5, T805-1994 of JTG E51-2009 "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" to determine the 7-day and 28-day infinite lateral compressive strength of the system.

[0039] 2. The solidified soil is crushed and pulverized to pass through a 0.5mm sieve, then dried to constant weight, and the free expansion rate is determined in accordance with GB_T50123-2019 "Standard for Geotechnical Testing Methods".

[0040] 3. Refer to Appendix B of CJT486-2015 "Soil Stabilizing Admixtures" to determine the water stability coefficient.

[0041] Example 1 series: In this series of examples, sepiolite powder from Preparation Example 1 is used as raw material, and different types and amounts of polyacrylamide are used to verify the system.

[0042] Example 1-1 specifically comprises the following components in parts by weight: 70 parts cement 20 parts calcium-based activator, specifically including 4 parts calcined gypsum and 16 parts quicklime. 15 parts fly ash 15 portions of lithium slag 8 parts reinforced short fiber 4 parts water-reducing agent 10 parts sepiolite Two parts of cationic polyacrylamide.

[0043] The preparation method of Example 1-1 is as follows: Mix all components except cationic polyacrylamide and water-reducing agent in a dry mixer for 1 minute. Then mix water and water-reducing agent together and add them to the mixture. Continue wet mixing for 8 minutes, controlling the flowability of the neat paste at 25°C to 170 mm (47 parts by weight of water). Set aside.

[0044] Based on Example 1-1, by substituting different types of polyacrylamide and the mass of sepiolite and polyacrylamide, and controlling the flowability to be similar, the examples shown in Table 1 can be obtained.

[0045]

[0046] Based on the above, experiments were conducted on the series of Examples 1, and the results are shown in Table 2.

[0047]

[0048] Based on the data in the table above, comparing Examples 1-1 and 1-11, and Examples 1-8 and 1-12, it can be seen that cationic polyacrylamide effectively reduces the free expansion rate and significantly improves the water stability coefficient in the system. Further analysis comparing Examples 1-2 and 1-7, where cationic and anionic polyacrylamide were substituted respectively, shows that using anionic polyacrylamide only slightly improves the water stability coefficient compared to the component without added polyacrylamide, while having virtually no effect on the free expansion rate. This demonstrates the significant role of cationic polyacrylamide in the above systems. In Examples 1-10, 1-13, and 1-14, the amount of polyacrylamide was further adjusted. It can be seen that excessive addition also leads to a certain decrease in the strength of the system, possibly due to excessive flocculation by the polyacrylamide, resulting in poor overall dispersion.

[0049] Based on the above, the amount of sepiolite powder was adjusted in Examples 1-15 to 1-18. It can be seen that in the scheme without sepiolite powder in Examples 1-18, although polyacrylamide provides certain water-blocking properties, its swelling inhibition effect is significantly weakened, and the strength is also significantly reduced.

[0050] Based on the above, further studies were conducted on Examples 1-1 to 1-6, in which the sepiolite modification method was adjusted to some extent. It can be seen that in Examples 1-4, the sepiolite powder was not calcined, resulting in a certain degree of decrease in overall strength. In Examples 1-5, without acid impregnation treatment, calcium ions were directly used to impregnate and load the sepiolite, leading to a lower calcium ion loading level in the system. This prevented the formation of a stable cross-linked structure in the solidified soil, resulting in a significant decrease in its free expansion rate and water stability coefficient, and a certain degree of decrease in overall strength. In Examples 1-8, no modification was performed on the sepiolite, and it showed a further trend of increased free expansion rate and decreased water stability coefficient compared to Examples 1-5. Furthermore, in Examples 1-6, calcium ions were loaded under acidic conditions, resulting in poor loading effect and similar experimental results to Examples 1-5. Long-term impregnation of sepiolite under acidic conditions easily led to structural loss of the sepiolite, resulting in a significant decrease in overall strength.

[0051] Example 2: Based on Examples 1-1, the selection and dosage of calcium-based activator in the system were adjusted. The corresponding experimental groups and experimental results are shown in Table 3.

[0052]

[0053] The experimental data in Table 3 show that the combination of gypsum and quicklime in the activator system provides better strength and improves the water stability of the system to a certain extent. Overall, quicklime and gypsum can improve the extrusion strength of the system, while gypsum can provide better stability in the system. However, excessive gypsum content can lead to unstable early gel formation and poor permeability to sepiolite, which ultimately affects the free expansion rate to a certain extent.

[0054] Example 3: Based on Examples 1-1, silica fume was further added. Examples and experimental results obtained with different amounts of silica fume are shown in Table 4.

[0055]

[0056] The above experiments show that adding silica fume to the scheme in Example 1-1 helps to significantly improve the early strength of the system, and also improves the overall strength to a certain extent. In addition, the addition of silica fume has a significant effect on improving the free expansion rate and water stability coefficient, but the improvement effect is not obvious after the dosage exceeds 10 parts, and there is even a slight decrease in strength. At the same time, it causes some loss of the fluidity of the system. Therefore, the dosage should not exceed 10 parts by mass.

[0057] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A water-stabilized, deformation-resistant curing agent suitable for expansive soil, characterized in that, It contains the following components according to parts by weight: 70 parts cement 15-30 parts of calcium-based activator 10-20 parts fly ash 5-10 parts sepiolite powder 10-20 parts of lithium slag 3-6 parts of water-reducing agent 1-3 parts of cationic polyacrylamide; The calcium-based activator is quicklime, gypsum, or a combination of both.

2. The water-stabilized, deformation-resistant curing agent for expansive soil according to claim 1, characterized in that, The sepiolite powder is pretreated using the following steps: Sepiolite powder is impregnated in an aqueous solution containing calcium ions or a mixed solution of water and alcohol containing calcium ions to induce calcium ion exchange.

3. The water-stabilized, deformation-resistant curing agent for expansive soil according to claim 2, characterized in that, The impregnation process of sepiolite powder is as follows: First, prepare an acidic solution with a pH of 2.5 to 4.5, add sepiolite to the solution for the first impregnation, and then add calcium ions to the system for the second impregnation.

4. The water-stabilized, deformation-resistant curing agent for expansive soil according to claim 3, characterized in that, When adding calcium ions to the system, calcium hydroxide should be used.

5. The water-stabilized, deformation-resistant curing agent for expansive soil according to claim 4, characterized in that, When the sepiolite is impregnated in the acid solution, the solid-liquid ratio of the sepiolite to the acid solution is 5-10 g: 100 mL, and / or, The acid immersion temperature is 50–80℃, the time is 5–10 min, and / or, The mass of the calcium hydroxide is 0.1 to 0.2 times the mass of the sepiolite, and / or, After the calcium hydroxide is added, the soaking time continues for 2 to 4 hours.

6. The water-stabilized, deformation-resistant curing agent for expansive soil according to claim 2, characterized in that, Before impregnation, the sepiolite powder is first calcined at a temperature of 300–500°C for 30–120 minutes.

7. The water-stabilized, deformation-resistant curing agent for expansive soil according to claim 1, characterized in that, The gypsum is calcined gypsum, and the gypsum accounts for 10-30% of the mass of the calcium-based activator.

8. The water-stabilized, deformation-resistant curing agent for expansive soil according to claim 1, characterized in that, It also contains 5 to 10 parts by weight of silica fume.

9. The water-stabilized, deformation-resistant curing agent for expansive soil according to claim 1, characterized in that, It also contains 5 to 10 parts by weight of reinforcing short fibers, wherein the length distribution of the reinforcing short fibers is 3 to 6 mm.

10. The method of using the water-stabilized, deformation-resistant curing agent for expansive soil according to any one of claims 1 to 9, characterized in that, After mixing the components of cationic polyacrylamide and water-reducing agent, add water and water-reducing agent to adjust the grout flowability to 120-200 mm at 25°C. Then add cationic polyacrylamide and spray, grout, or mix directly with the soil before curing.

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