Curing agent, composite modified silt material as well as preparation method and application of composite modified silt material

Abstract

The invention relates to the technical field of civil construction material preparation, in particular to a curing agent, a composite modified silt material and a preparation method and application of the composite modified silt material. The invention provides a curing agent. The curing agent is composed of rice husk carbon and lignin. The curing agent disclosed by the invention is added into silt, so that the recycling value of agricultural wastes of rice husks and lignin is fully utilized, the negative effects of high carbon emission and strong alkalinity of a traditional curing agent on the ecological environment are reduced, and the porous adsorption characteristic of rice husk carbon and an alkaline environment are cooperated with the ion exchange effect of Ca < 2 + > in lignin, so that the curing agent is more environmentally friendly. The calcium silicate hydrate is added into the silt to generate stable calcium silicate hydrate gelling substances, so that the compressive strength, shear strength and internal friction angle of the silt are remarkably improved, and meanwhile, microstructure degradation and mechanical property degradation caused by freeze-thaw cycle are effectively inhibited by filling pores and enhancing cohesive force among particles; therefore, efficient and green solidification and long-term stability improvement of the silt foundation in the cold region and innovative application of environment-friendly engineering materials are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering and building material preparation, and in particular to a curing agent, a composite modified silt material, and a preparation method and application thereof. Background Art

[0002] The key to managing silt roadbed diseases lies in solidifying the silt to increase its compressive strength, reduce its permeability, and minimize damage to the roadbed silt under freeze-thaw cycles. Currently, there are a variety of solidifying agents for silt, primarily organic, inorganic, and bio-enzyme. Inorganic solidifying agents include cement and lime. However, cement and lime are alkaline, and under strong alkaline conditions, they can affect the reproduction of surrounding flora and fauna. Organic solidifying agents include calcium lignin sulfonate and xanthan gum. Bio-enzyme solidifying agents include microbially induced calcium carbonate and cross-linked biopolymers. When using radioactively induced microorganisms, it is important to consider whether they pose a risk to humans and the environment. Therefore, with increasing concern about environmental issues, it is particularly important to find new soil stabilizers that are both economical and environmentally friendly. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention provides a curing agent, a composite modified silt material, and its preparation and application. This invention utilizes rice husk carbon and lignin as biomass materials and adds them to silt. This not only fully utilizes the resource value of rice husk and lignin agricultural waste, but also significantly improves the compressive strength, shear strength, and internal friction angle of the composite modified silt material.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: The first object of the present invention is to provide a curing agent, which is composed of rice husk carbon and lignin; the mass percentage of rice husk carbon to lignin is 5%~20%:3%~11%.

[0005] A second object of the present invention is to provide a method for preparing the above-mentioned curing agent, comprising the following steps: The rice husk is burned at 600-700 degrees Celsius to obtain rice husk carbon; the rice husk carbon is mixed with lignin to obtain a curing agent.

[0006] The third object of the present invention is to provide a composite modified silt material, which is composed of the above-mentioned curing agent and silt, the mass percentage of the curing agent is 8wt%~31wt%, the mass percentage of the silt is 69wt%~92wt%, and the sum of the mass percentages of the two is 100%.

[0007] Preferably, the dry density of the silt is 1.53 g / cm 3 ~1.60g / cm 3 , the moisture content is 15.9%~19.0%.

[0008] More preferably, the dry density of the silt is 1.60 g / cm 3 , the moisture content is 16.3%.

[0009] Preferably, the unconfined compressive strength of the composite modified silt material is 1384.55 kPa.

[0010] The fourth object of the present invention is to provide a method for preparing the composite modified silt material, comprising the following steps: mixing silt and a curing agent, placing the mixture in a mold for curing, and obtaining the composite modified silt material. During the curing process, SiO2 in rice husk carbon and Ca in lignin are 2+ The minerals in the silt react fully and form calcium silicate hydrate, which is a solid composite modified silt material.

[0011] The curing conditions are: standing at 23℃~25℃ and relative humidity 85%~98% for 7d~21d.

[0012] The fifth object of the present invention is to provide the use of the above-mentioned composite modified silt material in the preparation of a highway subbase. Compared with the prior art, the beneficial effects of the present invention are:

[0013] 1. The present invention provides a curing agent composed of rice husk carbon and lignin, with the mass ratio of rice husk carbon to lignin being 5-20:3-11. Compared to the inorganic, organic, and enzyme-based curing agents used in the prior art, the present invention utilizes rice husk carbon and lignin as biomass materials and adds them to silt as curing agents. This not only fully utilizes the resource value of rice husk and lignin agricultural waste, but also significantly improves the compressive and shear strengths of the silt. Furthermore, by filling pores and enhancing inter-particle adhesion, it effectively inhibits microstructural degradation and mechanical property loss caused by freeze-thaw cycles.

[0014] 2. The present invention provides a composite modified silt material, which is composed of a curing agent and silt, wherein the mass percentage of the curing agent is 8wt%~31wt%, the mass percentage of the silt is 69wt%~92wt%, and the sum of the mass percentages of the two is 100%. The composite modified silt material of the present invention has the advantages of high strength, freeze-thaw resistance, environmental friendliness and economy. Specifically, under the synergistic effect of rice husk carbon (15% addition) and lignin (11% addition), the 7-day unconfined compressive strength of the solidified soil reaches 1384.55 kPa, which is about 10 times higher than that of unsolidified soil. The peak shear strength is increased by 4 times (reaching 200 kPa at a confining pressure of 200 kPa), and the internal friction angle is stabilized at 28°. After experiencing 10 freeze-thaw cycles, the cohesion only decreases by 39.46%, and the residual strength remains at 66.87% of the unfreeze-thaw state. Its microstructure significantly inhibits freeze-thaw degradation (porosity only increases by 15%) due to the pores filled by CSH cementitious material. Combined with the resource utilization of agricultural waste (rice husk utilization rate >95%, cost reduction by 70%), high-efficiency, green and long-term cold-region silt foundation solidification can be achieved without complex processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Graphs showing the compressive strength peak values ​​of the composite modified silt materials of Examples 1 to 20 and the modified silt materials of Comparative Examples 1 to 9, wherein a represents Comparative Example 1 to 5, b represents Comparative Example 6 and Example 1 to 5, c represents Comparative Example 7 and Example 6 to 10, d represents Comparative Example 8 and Example 11 to 15, and e represents Comparative Example 9 and Example 16 to 20.

[0016] Figure 2 These are stress-strain curves of the composite modified silt materials of Examples 1 to 20 and the modified silt materials of Comparative Examples 1 to 9, wherein a represents Comparative Example 1 to 5, b represents Comparative Example 6 and Example 1 to 5, c represents Comparative Example 7 and Example 6 to 10, d represents Comparative Example 8 and Example 11 to 15, and e represents Comparative Example 9 and Example 16 to 20.

[0017] Figure 3 This is a graph of the unconfined compressive strength of the composite modified silt materials of Examples 1 to 20 and the modified silt materials of Comparative Examples 1 to 9.

[0018] Figure 4 Correlation analysis diagram of the compressive strength of stabilized soil, where a is the Person correlation analysis diagram and b is the Spearman correlation analysis diagram.

[0019] Figure 5The shear stress-shear displacement curves of silt and modified silt materials of Comparative Examples 1 to 5 are shown, where a is silt, b is Comparative Example 1, c is Comparative Example 2, d is Comparative Example 3, e is Comparative Example 4, and f is Comparative Example 5.

[0020] Figure 6 The shear stress-shear displacement curves of the modified silt material of Comparative Example 6 and the composite modified silt materials of Examples 1 to 5 are shown, wherein a is Comparative Example 6, b is Example 1, c is Example 2, d is Example 3, e is Example 4, and f is Example 5.

[0021] Figure 7 10 and 11. Shear stress-shear displacement curves of the composite modified silt materials of Examples 6 to 10 and the modified silt material of Comparative Example 7, wherein a is Comparative Example 7, b is Example 6, c is Example 7, d is Example 8, e is Example 9, and f is Example 10.

[0022] Figure 8 11 to 15 and the modified silt material of comparative example 8, wherein a is comparative example 8, b is example 11, c is example 12, d is example 13, e is example 14, and f is example 15.

[0023] Figure 9 The graphs of internal friction angle change and cohesion change of silt, composite modified silt materials of Examples 1 to 20, and modified silt materials of Comparative Examples 1 to 9 are shown. In particular, a is the graph of internal friction angle change, and b is the graph of cohesion change.

[0024] Figure 10 This is a stress-strain curve diagram of the composite modified silt material of Example 15 under different confining pressures.

[0025] Figure 11 This is a diagram of the elastic modulus of the composite modified silt material of Example 15 under different freeze-thaw cycles.

[0026] Figure 12 It is the relationship between the number of freeze-thaw cycles and the elastic modulus, as well as the fitting curve of the experimental value and the calculated theoretical value.

[0027] Figure 13 Schematic diagram of peak deviatoric stress, internal friction angle and cohesion under various confining pressures.

[0028] Figure 14 This is the relationship diagram between residual strength, confining pressure and number of freeze-thaw cycles.

[0029] Figure 15These are scanning electron microscope images of silt and the composite modified silt material of Example 15, where a is silt and b is the composite modified silt material.

[0030] Figure 16 These are scanning electron microscope images of the composite modified silt material of Example 15 at different freeze-thaw cycle numbers, where a represents 0 times, b represents 1 time, c represents 3 times, d represents 5 times, and e represents 10 times. DETAILED DESCRIPTION

[0031] The technical solutions of the present invention will be described clearly and completely below in conjunction with the data in the examples of the present invention. Obviously, the described examples are only a part of the embodiments of the present invention, rather than all of the embodiments. It should be noted that the various raw materials, reagents, instruments and equipment used in the following examples of the present invention can be purchased from the market or prepared by existing methods.

[0032] In the existing technology, traditional curing agents have problems such as environmental hazards, insufficient cost-effectiveness and waste of resources: inorganic curing agents release strong alkaline substances during the curing process, which changes the ecological balance of the soil in the long term; although organic curing agents reduce the alkaline hazards, they have high production costs and the curing stability is easily affected by dry-wet cycles; bio-enzyme curing agents rely on special bacterial culture or radioactive induction technology, which poses biosafety risks and process complexity.

[0033] To address the above-mentioned problems of the prior art, the present invention provides a curing agent composed of rice husk carbon and lignin, with the mass ratio of rice husk carbon to lignin being 5-20:3-11. The present invention overcomes the problems of the prior art through the synergistic curing mechanism of rice husk carbon and lignin.

[0034] Specifically, the strong alkalinity (pH>12) of inorganic curing agents (cement, lime) destroys the ecological balance of the soil. In the present invention, the weak alkaline environment (pH 8-9) formed by carbonization of rice husks and the Ca content of calcium lignin sulfonate are combined to form a 2+ The reaction produces CSH gel, which prevents soil alkalinization and reduces groundwater contamination. While enzyme curing agents rely on microbial activity and pose a risk of biocontamination, this invention employs purely physical and chemical curing, devoid of biologically active ingredients, eliminating biosafety risks. Furthermore, addressing the high cost of organic curing agents, this invention uses rice husks (a waste resource) and lignin (a bioethanol byproduct) as raw materials, reducing overall costs.

[0035] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments: Example 1 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 5:3 to obtain a curing agent. Subsequently, the curing agent is incorporated into the silt in a mass ratio of 8:92. After curing, a composite modified silt material, designated R5-L3, is obtained.

[0036] Example 2 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 5:5 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of 10:90 to the silt, and after curing, a composite modified silt material is obtained, which is designated as R5-L5.

[0037] Example 3 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 5:7 to obtain a curing agent; then, the curing agent is incorporated into the silt in a mass ratio of the curing agent to silt of 12:88. After curing, a composite modified silt material, designated R5-L7, is obtained.

[0038] Example 4 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 5:9 to obtain a curing agent. Subsequently, the curing agent is incorporated into the silt in a mass ratio of the curing agent to silt of 14:86. After curing, a composite modified silt material, designated R5-L9, is obtained.

[0039] Example 5 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 5:11 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of 16:84 to the silt, and after curing, a composite modified silt material is obtained, designated R5-L11.

[0040] Example 6 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 10:3 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of 13:87 to the silt. After curing, a composite modified silt material is obtained, which is designated as R10-L3.

[0041] Example 7 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 10:5 to obtain a curing agent; then, adding the curing agent to the silt in a mass ratio of 15:85. After curing, a composite modified silt material was obtained, which was recorded as R10-L5.

[0042] Example 8 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 10:7 to obtain a curing agent; then, adding the curing agent to the silt in a mass ratio of 17:83 to the silt, and curing the mixture to obtain a composite modified silt material, designated R10-L7.

[0043] Example 9 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 10:9 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of the curing agent to silt of 19:81. After curing, a composite modified silt material, designated R10-L9, is obtained.

[0044] Example 10 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 10:11 to obtain a curing agent; then, adding the curing agent to the silt in a mass ratio of the curing agent to silt of 21:79. After curing, a composite modified silt material, designated R10-L11, is obtained.

[0045] Example 11 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 15:3 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of 18:82 to the silt, and after curing, a composite modified silt material is obtained, designated R15-L3.

[0046] Example 12 A method for preparing a composite modified silt material, wherein rice husk carbon and lignin are mixed in a mass ratio of 15:5. The curing agent was mixed in a ratio of 20:80 to obtain a curing agent; then, the curing agent was added to the silt according to a mass ratio of the curing agent to the silt of 20:80. After curing, a composite modified silt material was obtained, which was recorded as R15-L5.

[0047] Example 13 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 15:7 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of the curing agent to silt of 22:78. After curing, a composite modified silt material, designated R15-L7, is obtained.

[0048] Example 14 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 15:9 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of 24:76 to the silt. Among them, after curing, a composite modified silt material is obtained, which is recorded as R15-L9.

[0049] Example 15 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 15:11 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of 26:74. Mix to obtain a curing agent; then, according to the mass ratio of curing agent to silt of 26:74, the curing agent is added to the silt, and after curing, a composite modified silt material is obtained, which is recorded as R15-L11.

[0050] Example 16 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 20:3 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of 23:77 to the silt, and after curing, a composite modified silt material is obtained, designated R20-L3.

[0051] Example 17 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 20:5 to obtain a curing agent; then, adding the curing agent to the silt in a mass ratio of 25:75 to the silt, and curing the mixture to obtain a composite modified silt material, designated R20-L5.

[0052] Example 18 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 20:7 to obtain a curing agent; then, the curing agent is added to the silt in a mass ratio of 27:73 between the curing agent and the silt, and curing the mixture to obtain a composite modified silt material, designated R20-L7.

[0053] Example 19 A method for preparing a composite modified silt material, wherein rice husk carbon and lignin are mixed in a mass ratio of 20:9. The curing agent was mixed to obtain a curing agent; then, the curing agent was added to the silt according to a mass ratio of the curing agent to the silt of 29:71. After curing, a composite modified silt material was obtained, which was recorded as R20-L9.

[0054] Example 20 A method for preparing a composite modified silt material comprises mixing rice husk carbon and lignin in a mass ratio of 20:11 to obtain a curing agent; then, adding the curing agent to the silt in a mass ratio of 31:69 to the silt, and curing the mixture to obtain a composite modified silt material, designated R20-L11.

[0055] Comparative Example 1 A method for preparing a modified silt material comprises adding lignin to silt at a mass ratio of lignin to silt of 3:97, and curing the silt to obtain the modified silt material, which is designated as R0-L3.

[0056] Comparative Example 2 A method for preparing a modified silt material is the same as the preparation method of Comparative Example 1, except that the amount of lignin added is replaced by 5% from 3%, to obtain a modified silt material, which is recorded as R0-L5.

[0057] Comparative Example 3 A method for preparing a modified silt material is the same as the preparation method of Comparative Example 1, except that the amount of lignin added is replaced by 7% from 3%, to obtain a modified silt material, which is designated as R0-L7.

[0058] Comparative Example 4 A method for preparing a modified silt material is the same as the preparation method of Comparative Example 1, except that the amount of lignin added is replaced by 9% from 3%, to obtain a modified silt material, which is designated as R0-L9.

[0059] Comparative Example 5 A method for preparing a modified silt material is the same as the preparation method of Comparative Example 1, except that the amount of lignin added is replaced by 11% from 3%, to obtain a modified silt material, which is designated as R0-L11.

[0060] Comparative Example 6 A method for preparing a modified silt material comprises adding rice husk carbon to silt in a mass ratio of 5:95, and curing the silt to obtain a modified silt material, which is designated as R5-L0.

[0061] Comparative Example 7 A method for preparing a modified silt material is the same as the preparation method of Comparative Example 6, except that the amount of rice husk carbon added is replaced from 5% to 10%, to obtain a modified silt material, which is recorded as R10-L0.

[0062] Comparative Example 8 A method for preparing a modified silt material is the same as the preparation method of Comparative Example 6, except that the amount of rice husk carbon added is replaced from 5% to 15%, to obtain a modified silt material, which is recorded as R15-L0.

[0063] Comparative Example 9 A method for preparing a modified silt material is the same as the preparation method of Comparative Example 6, except that the amount of rice husk carbon added is replaced from 5% to 20%, to obtain a modified silt material, which is recorded as R20-L0.

[0064] (1) Unconfined compressive strength: The silt, the composite modified silt materials of Examples 1 to 20, and the modified silt materials of Comparative Examples 1 to 9 were respectively placed in a mold to form a cylinder with a diameter of 39.1 mm and a height of 80 mm; then placed in a room with a curing temperature of 24°C and a relative humidity of 98% for 7 days, 14 days, and 21 days, respectively, and then the unconfined compressive strength was studied. The specific scheme is shown in Table 1.

[0065] Table 1 Test factors and variables observe Figure 1 The results show that, under the condition of a fixed rice husk carbon content, the unconfined compressive strength of the composite modified silt material gradually increases with increasing lignin content. In particular, when the lignin content reaches 11%, the strength of the composite modified silt material increases significantly, reaching 690.84 kPa, 715.74 kPa, 931.93 kPa, 1384.55 kPa, and 1395.17 kPa, respectively. Compared with the samples with the same rice husk carbon content and 9% lignin content, the strength increases are 88.90%, 89.74%, 78.60%, 102.31%, and 53.51%, respectively. Therefore, it is concluded that, under the condition of a fixed rice husk carbon content, the lignin content has a significant effect on the unconfined compressive strength of silt.

[0066] by Figure 1 For example, in Figure d, when the rice husk carbon content is fixed, the unconfined compressive strength of the composite modified silt material increases by 7.3%, 11.2%, 31.8%, 38.0%, 179.3%, and 157.5%, respectively, with increasing lignin content. Furthermore, when the rice husk carbon content is 15%, the unconfined compressive strengths at different lignin ratios are 6.10, 3.01, 3.07, 1.98, 1.87, 2.0, and 1.54 times that of the 0% rice husk carbon content; 1.75, 1.85, 1.85, 1.79, 1.81, 1.94, and 1.45 times that of the 5% rice husk carbon content; and 1.55, 1.66, 1.67, 1.48, 1.31, 1.49, and 1.29 times that of the 10% rice husk carbon content. This shows that the rice husk carbon content plays a key role in improving the unconfined compressive strength of the composite modified silt material, and with the increase of rice husk carbon content, the compressive strength of the composite modified silt material gradually increases.

[0067] Considering both economic efficiency and practical engineering needs, while ensuring that the compressive strength meets regulatory requirements, the preferred option is one with lower costs and satisfactory performance. Therefore, in subsequent freeze-thaw cycle experiments, a composite modified silt material containing 15% rice husk carbon and 11% lignin was selected to investigate its mechanical properties.

[0068] observe Figure 2 The results show that the stress-strain curves of the composite modified silt materials have a consistent trend, which indicates that the mechanical behavior of the composite modified silt materials is consistent during the stress process. With the increase of rice husk carbon content, the compressive strength of the composite modified silt materials gradually increases. Figure 2 Figure (a) shows that the peak strength gradually decreases with increasing lignin content. R0L3 has a higher peak strength but decreases more rapidly, while R0L5 and R0L7 have lower peak strengths but decrease more slowly. This indicates that the addition of lignin imparts better plasticity to the modified silt material.

[0069] Depend on Figure 2 Figure b shows that the primary deformation of the modified silt material is concentrated within the strain range of 3% to 6%. R5L0 reaches its peak strength near 3% strain and then rapidly declines, demonstrating strong initial compressive resistance but poor durability. This indicates that the combined action of rice husk carbon and lignin forms a stable calcium silicate structure in the silt, significantly improving the long-term stability and compressive resistance of the composite modified silt material.

[0070] Depend on Figure 2 Figure c shows that R10L11 reaches about 950kPa at a strain of 3%, and its compressive strength gradually increases with the increase of lignin content. Figure 2 In Figure d, R15L11 exhibits the highest compressive strength. Further analysis shows that increasing the lignin content increases the compressive strength by 7.3%, 11.2%, 31.8%, 38.0%, and 179.3%, respectively. This indicates that the rice husk carbon and lignin interact to form a stable calcium silicate structure in the silt, significantly improving the long-term stability and compressive properties of the composite modified silt material.

[0071] observe Figure 3 It was found that under the same curing age, the unconfined compressive strength of silt gradually increased with the increase of rice husk carbon and lignin content. This indicates that the Ca 2+ Under the combined action of SiO2 released from rice husk carbon and the alkaline environment, it reacts chemically with the charged particles in the silt to generate CaSiO3 and charged plasmid clusters.

[0072] Under different curing age conditions, the unconfined compressive strength of the composite modified silt material with a rice husk carbon content of 20% and a lignin content of 11% showed the best value. This is because the extension of the curing age provides the best conditions for the SiO2 in the rice husk carbon and the Ca2+ provided by the lignin. 2+The reaction between the two materials provides sufficient time for the curing effect to be fully realized. However, according to the "Highway Asphalt Pavement Design Specifications," when the curing agent content is no less than 8%, the unconfined compressive strength at 7 days must be between 1.0 MPa and 2.0 MPa to meet the requirements for the subbase of secondary and lower highways with medium traffic volume. Further research has shown that when the rice husk carbon content is 15% and the lignin content is 11%, the unconfined compressive strength of the composite modified silt material reaches 1384.55 kPa within 7 days of curing, meeting the specification requirements.

[0073] A. Significance analysis of the effects of rice husk carbon, lignin content, and curing age on compressive strength: In order to further study whether the effects of rice husk carbon, lignin content and curing age on the uniaxial compressive strength of cured silt are significant, and the extent of the influence of the three factors on the unconfined compressive strength of silt, the significance analysis of the obtained test results was carried out.

[0074] Three factors were set: rice husk carbon content (R), lignin content (L), and curing age (D). The rice husk carbon factor included four levels, the lignin factor included six levels, and the curing age factor included three levels. i , L j 、D k ) The test result is recorded as x ijk .

[0075] (1) (2) (3) (4) (5) Total variance sum of squares and variance sum of squares of each factor (6) (7) Variance estimates for each factor (8) According to the above formulas 1 to 8, the significance analysis of the effects of rice husk carbon, lignin and curing age on the compressive strength of silt is obtained in Table 2.

[0076] Table 2 Significance analysis of the effects of rice husk carbon, lignin and curing age on the compressive strength of silt Table 2 shows that rice husk carbon content has the most significant impact on compressive strength, with an F-value of 15.763, far higher than the other two factors, indicating that rice husk carbon content has a strong influence on the compressive strength of silt. Secondly, the F-value of lignin content is 13.505, which, although lower than that of rice husk carbon content, still has an impact. Curing age has the least impact on the compressive strength of silt, with an F-value of 1.332, indicating that its impact on compressive strength is not statistically significant. This means that in the actual soil solidification process, adjusting the rice husk carbon content and lignin content is more effective in improving compressive strength than extending the curing age.

[0077] B. Correlation analysis between rice husk carbon, lignin content and curing age on compressive strength: The present invention uses Person correlation analysis and Spearman rank correlation analysis to systematically analyze the effects of rice husk carbon, lignin content and curing age on the compressive strength of silt. Figure 4 The results show.

[0078] from Figure 4 Figure (a) shows the strongest correlation between lignin content and silt compressive strength, indicating that its addition significantly improves silt properties. Lignin's unique chemical structure and physical properties enhance its strength during the soil consolidation process. This result is consistent with the trend in the F-value analysis, further confirming that lignin has a greater impact on compressive strength than rice husk carbon.

[0079] from Figure 4 Figure (b) shows that the compressive strength of silt increases with increasing rice husk carbon content, lignin content, and curing age, indicating that all three factors have a positive impact on the compressive strength of silt. Specifically, lignin content has the greatest impact on compressive strength, followed by rice husk carbon content, while curing age has the least impact. Therefore, in practical applications, optimizing the content of rice husk carbon and lignin is more critical than simply extending the curing time to improve the compressive properties of silt.

[0080] (2) Shear strength: The volume of silt required in the shear box was determined based on the silt's density and shear volume parameters. The silt, the composite modified silt materials from Examples 1 to 20, and the modified silt materials from Comparative Examples 1 to 9 were each formed into annular bodies with a diameter of 61.8 mm and a height of 20 mm. After sample preparation, the specimens were placed in a curing chamber for curing at a temperature of 24°C ± 1°C and a relative humidity of 98%. The curing periods were 7 days, 14 days, and 21 days, respectively. The specific curing schedule is shown in Table 1.

[0081] observe Figure 5The results showed that, at the same rice husk carbon content, the shear strength of silt showed a significant upward trend with increasing vertical pressure (100 kPa, 200 kPa, and 300 kPa). This suggests that increasing vertical pressure can promote the compaction of the silt structure, thereby improving the shear strength of the silt. Furthermore, the lignin content significantly affects the shear strength of the silt. Under the same vertical load, the shear strength of the silt increases with increasing lignin content.

[0082] Depend on Figure 6 The results show that as the shear displacement increases, the shear stress shows an overall upward trend, and the growth trend of shear stress is particularly significant when the vertical load is 300 kPa. This shows that as the applied shear displacement increases, the shear stress of the silt continues to increase, especially under higher vertical loads, where the shear resistance of the silt becomes more pronounced.

[0083] Depend on Figure 7 The results showed that increasing the amount of rice husk carbon to 10% significantly improved the shear resistance of the silt. This is because the rice husk carbon, while providing an alkaline environment, promotes the effective bonding between lignin and the silt, thereby generating more cementitious materials and providing better structural support for the silt.

[0084] Depend on Figure 8 It is concluded that with the increase of shear displacement, the shear stress gradually increases, reflecting that the CaSiO3 substance generated in the silt structure can effectively resist the action of shear force, thereby improving the shear strength of the silt.

[0085] Depend on Figure 9 Figure (a) shows that the internal friction angle exhibits different trends with increasing lignin content, and this trend is closely related to the rice husk carbon content. When the rice husk carbon content is 0%, the internal friction angle of the composite modified silt material first increases and then decreases with increasing lignin content. The increase in the internal friction angle is particularly significant at a 7% lignin content, indicating that within this content range, the interaction between lignin and silt significantly improves the mechanical properties of the composite modified silt material. When the rice husk carbon content is 5%, the internal friction angle of the composite modified silt material gradually increases with increasing lignin content. This indicates that in the alkaline environment provided by the rice husk carbon, lignin can effectively react with the silt material, forming a cementing agent that strengthens the structure of the composite modified silt material, thereby increasing the friction and cohesion between the composite modified silt material particles. When the rice husk carbon content is 10% and 15%, the increase in the internal friction angle of the composite modified silt material tends to stabilize with increasing lignin content. This indicates that at higher rice husk carbon content, the structure of the composite modified silt material has become relatively stable, and the further incorporation of lignin gradually weakens the improvement effect on the internal friction angle.

[0086] Depend on Figure 9 Figure b shows that when the rice husk carbon content is 0% and 10%, the internal cohesion of the composite modified silt material becomes more dispersed as the lignin content increases. However, when the rice husk carbon content is 5% and 15%, the internal cohesion of the composite modified silt material gradually increases with the increase in lignin content. This indicates that the increase in rice husk carbon enhances the alkaline environment within the composite modified silt material, thereby promoting better bonding and cementation between lignin and silt.

[0087] Depend on Figure 10 The results show that, when the confining pressure remains constant, the peak deviatoric stress gradually increases with the number of freeze-thaw cycles. The stress-strain curve rises rapidly when the axial strain ranges from 0 to 2.5%. At 2.5% axial strain, the peak deviatoric stress stabilizes. This stability is due to the fact that as the concentrated load increases, the bounding particles reach their maximum capacity to resist the external load. With increasing freeze-thaw cycles and confining pressure, the composite modified silt material is subjected to external compression, resulting in a decrease in internal bonding strength.

[0088] Depend on Figure 11 The results show that while the trend in the elastic modulus of silt that has undergone multiple freeze-thaw cycles is similar to that of the composite modified silt material that has not undergone freeze-thaw cycles, the two show significant differences due to the destructive effects of freeze-thaw cycles on the structure of the composite modified silt material. The study found that the elastic modulus is significantly negatively correlated with the number of freeze-thaw cycles. That is, as the number of freeze-thaw cycles increases, the elastic modulus of the composite modified silt material continues to decrease, but the rate of this decrease gradually slows with the increase in the number of freeze-thaw cycles and eventually stabilizes.

[0089] Depend on Figure 12 The results show that confining pressure plays an important role in the change of elastic modulus of composite modified silt material, and the elastic modulus of composite modified silt material also decays at different rates with the increase of freeze-thaw cycles.

[0090] Depend on Figure 13The results of peak deviatoric stress under different confining pressures show that under the same confining pressure conditions, with the increase of the number of freeze-thaw cycles, the peak deviatoric stress of the sample shows a significant downward trend, but its decreasing rate gradually slows down. When the confining pressure is 100kPa, the peak deviatoric stress of the composite modified silt material decreased by 8.9% after one freeze-thaw cycle, decreased by 18.87% after three freeze-thaw cycles, decreased by 21.08% after five freeze-thaw cycles, and decreased by 28.72% after ten freeze-thaw cycles; when the confining pressure is 200kPa; the peak deviatoric stress of the composite modified silt material decreased by 9.1% after one freeze-thaw cycle, decreased by 18.80% after three freeze-thaw cycles, decreased by 33.77% after five freeze-thaw cycles, and decreased by 77% after ten freeze-thaw cycles. .29%; at a confining pressure of 300 kPa, the peak deviatoric stress of the composite-modified silt material decreased by 6.7% after one freeze-thaw cycle, 16.86% after three freeze-thaw cycles, 20.81% after five freeze-thaw cycles, and 36.38% after ten freeze-thaw cycles. Under a confining pressure of 500 kPa, the peak deviatoric stress of the composite-modified silt material decreased by 19.18% after one freeze-thaw cycle, 24.43% after three freeze-thaw cycles, 32.28% after five cycles, and a further 38.32% after ten freeze-thaw cycles. This trend indicates that the effects of freeze-thaw cycles on soil strength primarily occur in the initial stages. As the number of cycles increases, the damage to the soil's internal structure stabilizes, and the decrease in peak deviatoric stress gradually slows. This decreasing trend in peak deviatoric stress is closely related to the damage to the soil's internal microstructure caused by freeze-thaw cycles.

[0091] Depend on Figure 13 The results of the change of the internal friction angle under the freeze-thaw cycle show that the internal friction angle of the sample gradually decreases with the increase of the freeze-thaw cycle number. When the freeze-thaw cycle number gradually increases, the internal friction angle decreases by 3.58%, 10.69%, 15.00%, and 30.08%, respectively. This is because the connection mode of the particles inside the sample changes after freeze-thaw, and the load causes the position of the silt particles solidified by rice husk carbon-lignin to shift, and the internal friction angle fluctuates. In addition, Figure 13 Results from studies of cohesion under moderate freeze-thaw cycles show that cohesion gradually decreases with increasing freeze-thaw cycles. Cohesion decreased by 15.62%, 21.96%, 35.74%, and 39.46%, respectively, with increasing freeze-thaw cycles. Rice husk carbon-lignin incorporated into silt fills or encapsulates soil particles. As the number of freeze-thaw cycles increases, the bond between the curing agent and the silt gradually weakens, weakening the gelling effect and resulting in a gradual decrease in cohesion.

[0092] Depend on Figure 14 The results show that at a confining pressure of 100 kPa, the residual strength decreased by 6.6% after one freeze-thaw cycle, 19.56% after three freeze-thaw cycles, 20.67% after five freeze-thaw cycles, and 33.13% after ten freeze-thaw cycles. At a confining pressure of 200 kPa, the ratio of the failure strength to the failure strength of the unfrozen soil layer increased by 6.73%, 16.77%, 32.49%, and 55.54%, respectively, with increasing freeze-thaw cycles. At a confining pressure of 300 kPa, the ratio of the failure strength to the failure strength of the unfrozen soil layer increased by 9.8%, 16.47%, 22.34%, and 41.65%, respectively, with increasing freeze-thaw cycles. During the first few freeze-thaw cycles, due to the low number of cycles, the soil particles were bonded to the rice husk carbon and lignin by water, resulting in relatively little change in the failure strength.

[0093] observe Figure 15 From Figure a in the figure, it can be seen that the connection between the silt particles in the unconsolidated silt is relatively small, there are no cracks and pores on the surface, and the microstructure is relatively dense. Figure 15 Figure b shows that in the composite modified silt material after being solidified with rice husk carbon and lignin, flocculent polymers are attached around the small pores on its surface. This is the result of the full reaction of the curing agent, which produces a large amount of unevenly distributed hydrates around the pores. No large pores appear in the composite modified silt material.

[0094] Depend on Figure 16 Figures a and b in the figure show that after a freeze-thaw cycle, although large pores and flocculent polymers appear on the surface of the silt, the overall structure is not immediately severely damaged, showing its anti-freeze-thaw ability. Figure 16 Figures c and d in the figure show that when the silt undergoes 3 and 5 freeze-thaw cycles, the pores and cracks on its surface gradually increase and expand. This shows that the damage to the silt surface is gradual rather than a one-time destruction. Figure 16 Figures e and f show that until the silt has undergone 10 freeze-thaw cycles, repeated freeze-thaw cycles cause ice crystals to reshape and grow, disrupting the bond between the surface polymers and particles. This weakens the bond between them and reduces the amount of flocculent polymers available to fill the pores. Even after the ice crystals melt, the polymers cannot be restored, indicating that freeze-thaw cycles irreversibly damage the soil structure.

[0095] It is obvious that those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications of the present invention fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A curing agent, characterized in that The curing agent consists of rice husk carbon and lignin, and the mass ratio of the rice husk carbon to the lignin is 5-20:3-11.

2. A method for preparing the curing agent according to claim 1, characterized in that: The rice husk is burned at 600-700 degrees Celsius to obtain rice husk carbon; the rice husk carbon is mixed with lignin to obtain a curing agent.

3. A composite modified silt material, characterized in that: The invention is composed of the curing agent according to claim 1 and silt, wherein the mass percentage of the curing agent is 8wt% to 31wt%, the mass percentage of the silt is 69wt% to 92wt%, and the sum of the mass percentages of the curing agent and the silt is 100%.

4. The composite modified silt material according to claim 3, characterized in that: The dry density of silt is 1.53 g / cm 3 ~1.60g / cm 3 , the moisture content is 15.9%~19.0%.

5. The composite modified silt material according to claim 3, characterized in that: The unconfined compressive strength of the composite modified silt material is 1384.55 kPa.

6. A method for preparing the composite modified silt material according to any one of claims 3 to 5, characterized in that: The method comprises the following steps: mixing silt and a curing agent, placing the mixture in a mold for curing, and obtaining a composite modified silt material.

7. The method for preparing the composite modified silt material according to claim 6, characterized in that: The curing conditions are: standing at 23℃~25℃ and relative humidity 85%~98% for 7d~21d.

8. Use of the composite modified silt material according to claim 3 in preparing a highway subbase.

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