An expansive soil based on organic-inorganic composite modification and carbonation curing and its preparation method

Abstract

This invention discloses an expansive soil based on organic-inorganic composite modification and carbonization curing, and its preparation method, belonging to the field of materials technology. The expansive soil is prepared by carbonization curing of expansive soil, solid waste, and a modifier. The solid waste accounts for 15-60% of the total mass of the expansive soil and solid waste, and the modifier accounts for 0.1-5% of the total mass of the expansive soil and solid waste. The solid waste includes at least two of the following: fly ash, steel slag powder, mineral powder, carbide slag, red mud, and desulfurization ash. The modifier includes at least two of the following: water glass, urea, caustic soda, hexadecyltrimethylammonium bromide, and organosilicon waterproofing agent. This invention achieves efficient diffusion and reaction of CO2 in expansive soil through the synergistic effect of organic-inorganic composite modification and precise carbonization curing, forming a triple protective structure of carbonate-gel-hydrophobic film, thus achieving the dual goals of improving the engineering properties of expansive soil and reducing carbon emissions.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to an expansive soil based on organic-inorganic composite modification and carbonization curing, and its preparation method. Background Technology

[0002] my country is one of the countries where expansive soil is widely distributed. Expansive soil is a clay-like component, mainly composed of hydrophilic minerals such as montmorillonite, illite, and kaolinite. It exhibits significant water absorption and swelling, water loss and shrinkage, and strength reduction. Due to the harmful effects of expansive soil on buildings, it is often referred to as a "hidden disaster." According to incomplete statistics, the losses caused by expansive soil worldwide exceed US$5 billion annually. Therefore, the issue of expansive soil has long attracted great attention from the international and domestic engineering communities. Currently, solidifying agents that can effectively improve the engineering properties of expansive soil are mainly divided into four categories: inorganic, organic, composite, and biological. However, related research and application are still in the experimental and exploratory stage, and the reinforcement mechanism is still unclear, which seriously restricts the application of new solidifying agents in expansive soil areas.

[0003] Currently, the most common chemical modification method for expansive soil involves adding a certain amount of cement or lime as a binder. Through hydration and hardening reactions, this reduces soil expansibility, enhances soil strength, and has good long-term effectiveness. Patent CN110117421A discloses an expansive soil modifier, whose technical solution comprises the following components by weight: 5-10 parts carboxylated cationic resin liquid, 10-20 parts quicklime powder, 9-15 parts bauxite powder, 8-16 parts glass fiber powder, 2-3 parts surfactant, and 150-200 parts water. This modifier, by introducing the synergistic effect of organic polymer resin and inorganic mineral filler, makes expansive soil particles less prone to binding with water molecules and promotes solidification into a dense, plate-like structure. However, this method mainly relies on traditional inorganic materials for alkali-activated reactions and does not involve a carbonation curing process, making it difficult to effectively utilize carbon dioxide for environmentally friendly solidification. Patent CN113621380A discloses an ecological modifier for expansive soil, mainly prepared by dissolving and mixing purified water, polyaluminum chloride, penetrant JFC-2, and strong acid cation exchange resin, claiming to modify expansive soil into non-expansive soil. Although this scheme emphasizes "ecological" attributes and uses a combination of some inorganic salts and organic surfactants, its modification mechanism is still concentrated on ion exchange and physical encapsulation, lacking the construction of an organic-inorganic synergistic cross-linked network structure. Therefore, it has limitations in improving the long-term stability of expansive soil and realizing the resource utilization of low-carbon solid waste.

[0004] Therefore, there is an urgent need for a green modification technology that can effectively suppress the expansibility of expansive soil, improve its strength, and realize the resource utilization of solid waste and CO2 sequestration. Summary of the Invention

[0005] One of the objectives of this invention is to provide an expansive soil based on organic-inorganic composite modification and carbonization curing, which solves the problems of uneven modification effect, low carbonization efficiency and poor eco-friendliness of expansive soil in the prior art.

[0006] The second objective of this invention is to provide a method for preparing expansive soil based on organic-inorganic composite modification and carbonization curing, for use in preparing the aforementioned expansive soil based on organic-inorganic composite modification and carbonization curing.

[0007] The objective of this invention can be achieved through the following technical solutions: An expansive soil based on organic-inorganic composite modification and carbonization curing is prepared by carbonization curing of expansive soil, solid waste and modifier, wherein the solid waste accounts for 15-60% of the total mass of expansive soil and solid waste, and the modifier accounts for 0.1-5% of the total mass of expansive soil and solid waste; the solid waste includes at least two of fly ash, steel slag powder, mineral powder, carbide slag, red mud and desulfurization ash; the modifier includes at least two of water glass, urea, caustic soda, hexadecyltrimethylammonium bromide and organosilicon waterproofing agent.

[0008] By constructing an organic-inorganic composite modification system, the active silica-alumina components and calcium and magnesium ions in solid waste are utilized to form a stable carbonate and silica-alumina gel network under specific carbonation conditions. Simultaneously, an organic modifier modifies the soil surface, achieving precise control of the expansive soil's microstructure. This ratio ensures that the solid waste provides sufficient active ingredients for the carbonation reaction without causing a decrease in soil strength due to excessive amounts; the modifier dosage effectively adjusts the system's pH and surface properties while avoiding excessive amounts that could negatively impact the carbonation reaction.

[0009] Furthermore, the solid waste contains at least one calcium-containing material (such as steel slag powder, carbide slag, desulfurization ash) and one silicon-aluminum-containing material (such as fly ash, mineral powder, red mud), with a mass ratio of (1-3):1. The calcium-containing material provides Ca. 2+ Mg 2+ Plasma reacts with CO2 to generate carbonate precipitate, while silicon-aluminum materials provide SiO2 and Al2O3 to participate in the formation of silicon-aluminum gel. The two work together to construct a dual-reinforcement network.

[0010] Furthermore, the modifier comprises at least one inorganic modifier (water glass, urea, caustic soda) and one organic modifier (hexadecyltrimethylammonium bromide, organosilicon waterproofing agent), with a mass ratio of (2-4):1. The inorganic modifier adjusts the pH of the system and promotes the carbonization reaction, while the organic modifier modifies the soil surface through hydrophobic groups, thereby improving the waterproofing performance.

[0011] Furthermore, during the carbonation curing process, the CO2 pressure is 0.5-2 MPa, the temperature is 25-35℃, the relative humidity is 55-65%, and the CO2 concentration is 40-99%. This combination of parameters achieves an optimal balance between the carbonation reaction kinetics and thermodynamics: if the pressure is too low, the CO2 solubility will be insufficient, while if it is too high, energy consumption will increase and may lead to soil structural damage; if the temperature is too low, the reaction rate will be slow, while if it is too high, the CO2 solubility will decrease; if the humidity is too low, it will be unfavorable for ion migration, while if it is too high, it will reduce the CO2 partial pressure; if the concentration is too low, the reaction efficiency will be low, while if it is too high, the economy will be poor.

[0012] Furthermore, during the carbonization curing process, the CO2 pressure and temperature satisfy the following relationship: P = 0.02T + 0.35, where P is the pressure (MPa) and T is the temperature (°C). This relationship ensures that the solubility of CO2 in the soil and the reaction rate are optimally matched.

[0013] Furthermore, during the carbonization curing process, the relative humidity and CO2 concentration satisfy the following relationship: H = -0.35C +82.5, where H is the relative humidity (%) and C is the CO2 concentration (%). This relationship ensures a sufficient supply of water molecules as the reaction medium, while maintaining a sufficient CO2 partial pressure.

[0014] Furthermore, the mass ratio of hexadecyltrimethylammonium bromide to the organosilicon waterproofing agent in the organic modifier is (1-3):1. Hexadecyltrimethylammonium bromide reduces the electric double layer thickness of clay minerals through cation exchange, while the organosilicon waterproofing agent forms a hydrophobic film; the two work synergistically to enhance waterproofing performance.

[0015] Secondly, a method for preparing expansive soil based on organic-inorganic composite modification and carbonation curing includes the following steps: S1. Material pretreatment: Weigh out expansive soil, solid waste, and modifier according to the specified proportions, where solid waste accounts for 15-60% of the total mass of expansive soil and solid waste, and modifier accounts for 0.1-5% of the total mass of expansive soil and solid waste; S2. Mixing and blending: Mix the materials from step S1 in a mixing container for 5-30 minutes to form a homogeneous mixture; S3. Carbonization curing: Introduce CO2 into the mixing container, control the carbonization pressure at 0.5-2MPa, the temperature at 25-35℃, the relative humidity at 55-65%, and the CO2 concentration at 40-99%, and continue the carbonization reaction. S4. Curing treatment: Curing the carbonized mixture for 8-36 hours to allow the reaction to proceed fully and obtain modified expansive soil.

[0016] The key lies in the precise control of parameters during the S3 carbonization curing process. In the initial stage of carbonization (0-30 min), the system pH is relatively high (8.5-9.5), and CO2 mainly reacts with OH groups in the system. - The reaction produces HCO3 - As the reaction proceeds, the pH gradually decreases to 7.5-8.5, at which point CO2 and Ca... 2+ Mg 2+ The reaction produces CaCO3 and MgCO3 precipitates; simultaneously, SiO2 and HCO3 in the water glass... - The reaction produces a silica-alumina gel. This process creates an "alkaline-neutral" pH gradient, which ensures efficient CO2 absorption while avoiding reaction stagnation caused by a sudden drop in pH.

[0017] Furthermore, in step S1, the liquid limit of the expansive soil is 45-65%, the plasticity index is 20-35, and the free swelling rate is 40-80%, which represents a typical highly expansive soil.

[0018] Furthermore, the carbonization reaction in step S3 lasts for 1-4 hours. If the reaction time is too short, the carbonization will be insufficient, and if it is too long, there will be no significant gain and energy consumption will increase.

[0019] Furthermore, in step S4, the ambient temperature for the curing process is 20-30℃ and the relative humidity is 70-85%, which is conducive to the continued reaction of unreacted substances and structural stability.

[0020] The beneficial effects of this invention are: (1) This invention achieves a balance between the supply of active ingredients and the engineering properties of the soil by limiting the proportion of solid waste to 15-60% of the total mass of expansive soil and solid waste. Within this range, the solid waste can provide sufficient active silicon-aluminum and calcium-magnesium components to participate in the carbonization reaction and construct a stable microstructure network, while avoiding the problems of insufficient reaction due to too low a dosage or loose soil structure due to too high a dosage. This proportion range ensures that the active components in the solid waste can fully participate in the reaction to form an effective reinforcement network, while maintaining the basic engineering properties of the soil.

[0021] (2) This invention limits the modifier to a range of 0.1-5% of the total mass of expansive soil and solid waste, achieving precise control of the system environment. At this ratio, the modifier can effectively adjust the pH of the system to a suitable range, which not only promotes the carbonization reaction but also avoids reaction inhibition caused by excessive modifier. An appropriate amount of modifier can optimize the surface properties of the soil, enhance the interfacial bonding between organic and inorganic components, and improve the overall stability and durability of the modified soil.

[0022] (3) This invention uses at least two solid wastes selected from fly ash, steel slag powder, mineral powder, carbide slag, red mud, and desulfurization ash to construct a dual-reinforcement network through the complementary effects between different wastes. Calcium-containing materials provide Ca... 2+ Mg 2+ Plasma reacts with CO2 to form carbonate precipitates, which fill soil pores; the silica-alumina materials provide SiO2 and Al2O3 to participate in the formation of silica-alumina gel, which encapsulates soil particles and enhances water stability. The synergistic effect of the two materials systematically improves the soil microstructure, significantly enhancing the soil's mechanical properties and durability.

[0023] (4) This invention employs a combination of at least two modifiers selected from water glass, urea, caustic soda, hexadecyltrimethylammonium bromide, and organosilicon waterproofing agent to achieve a synergistic effect of inorganic-organic modification. The inorganic modifier promotes the carbonation reaction by adjusting the pH of the system and providing reactive components, while the organic modifier reduces water sensitivity by modifying the soil surface. The synergistic effect of the two forms an "alkaline-neutral" pH gradient change, which ensures efficient CO2 absorption and avoids reaction stagnation caused by a sudden drop in pH, making the carbonation reaction more complete and uniform.

[0024] (5) This invention forms a triple protective structure of "carbonate-gel-hydrophobic membrane" through the synergistic effect of organic-inorganic composite modification and carbonation curing. Carbonate precipitation fills the pores to improve compaction, the silica-alumina gel network enhances water stability, and the organic hydrophobic membrane reduces water sensitivity. The combined effect of these three factors effectively inhibits the swelling and shrinkage deformation of expansive soil. At the same time, this technical solution maintains the soil pH within an eco-friendly range, which is conducive to vegetation restoration, and achieves effective CO2 fixation, thus balancing engineering benefits and environmental benefits. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0026] Throughout the preparation process, precise control of each process parameter is crucial to the final modification effect. For example, the carbonization pressure and temperature must satisfy the relationship P=0.02T+0.35 to ensure the optimal match between CO2 solubility and reaction rate; the relative humidity and CO2 concentration must satisfy the relationship H=-0.35C+82.5 to ensure a sufficient supply of water molecules as the reaction medium while maintaining adequate CO2 partial pressure; the mass ratio of calcium-containing materials to silicon-aluminum-containing materials in the solid waste must be controlled within the range of (1-3):1 to construct an effective dual-reinforcement network; and the mass ratio of inorganic modifiers to organic modifiers in the modifier should be (2-4):1 to achieve synergistic optimization of strength improvement and waterproof performance.

[0027] If the carbonation pressure exceeds 2 MPa, it will lead to soil structural damage and a decrease in strength; if it is below 0.5 MPa, the CO2 solubility will be insufficient, and the carbonation reaction will be incomplete. If the temperature is above 35℃, the CO2 solubility will decrease significantly, and the reaction efficiency will decrease; if it is below 25℃, the reaction kinetics will be limited, and the reaction time will be prolonged. If the relative humidity is below 55%, insufficient water molecules will affect ion migration; if it is above 65%, the CO2 partial pressure will decrease, affecting the reaction rate. If the CO2 concentration is below 40%, the reaction efficiency will be low; if it is above 99%, the economics will be poor and there will be no significant gain.

[0028] The modified expansive soil prepared by this invention consists of three parts: first, carbonate precipitates (CaCO3, MgCO3) fill the soil pores and improve compaction; second, a silica-alumina gel network encapsulates soil particles to enhance water stability; and third, a hydrophobic film formed by organic modifiers reduces water sensitivity. These three components work synergistically to give the modified expansive soil high strength, low expansibility, and good ecological compatibility.

[0029] In the technical solution described in this invention, all operational steps, material ratios, and process parameters are essential technical features for achieving the desired technical effect, and none can be omitted. If the carbonation and curing step is omitted, stable carbonate precipitates cannot be formed, significantly reducing the modification effect; if only a single type of modifier is used, it is difficult to simultaneously achieve both strength and waterproofing performance; if the solid waste content exceeds the range of 15-60%, it will lead to the deterioration of the soil's engineering properties. Therefore, this invention achieves a systematic breakthrough in expansive soil modification technology through the synergy of organic-inorganic composite modification and precise carbonation and curing.

[0030] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0031] Example 1

[0032] This embodiment provides an expansive soil based on organic-inorganic composite modification and carbonation curing, which is prepared through the following steps: S1. Material Pretreatment: Weigh 100 kg of expansive soil with a liquid limit of 55%, a plasticity index of 28, and a free expansion rate of 65%, 30 kg of fly ash (containing silicon and aluminum materials), and 15 kg of steel slag powder (containing calcium materials), with a mass ratio of 2:1; weigh 1.5 kg of water glass (inorganic modifier) ​​and 0.5 kg of hexadecyltrimethylammonium bromide (organic modifier), with a mass ratio of 3:1; the amount of solid waste accounts for 30% of the total solid mass, and the amount of modifier accounts for 2% of the total solid mass.

[0033] S2. Mixing and blending: Mix the above materials in a forced mixer at 60 rpm for 10 minutes to form a homogeneous mixture.

[0034] S3. Carbonization and curing: Transfer the mixture to the carbonization reactor, introduce CO2, control the carbonization pressure at 0.6 MPa (which conforms to P=0.02×25+0.35=0.85, but the actual pressure should be slightly lower to verify the parameter boundaries), temperature at 25℃, relative humidity at 55%, CO2 concentration at 45%, and continue carbonization for 2 hours.

[0035] S4. Curing treatment: Transfer the carbonized mixture to a sealed bag and cure it for 12 hours at 25°C and 75% relative humidity to obtain modified expansive soil.

[0036] Example 2

[0037] The difference between this embodiment and Example 1 is as follows: the amount of fly ash added is 20 kg, the amount of steel slag powder added is 20 kg, and the amount of solid waste added accounts for 40% of the total solid mass; the amount of water glass added is 2.4 kg, and the amount of organosilicon waterproofing agent added is 0.8 kg, with a mass ratio of 3:1; the carbonization pressure is 1.0 MPa (meeting P=0.02×30+0.35=0.95), the temperature is 30℃, the relative humidity is 65%, the CO2 concentration is 80%, and the carbonization time is 3 hours. The remaining raw materials and preparation process are the same as in Example 1.

[0038] Example 3

[0039] The difference between this embodiment and Example 1 is as follows: the fly ash content is 15 kg, the mineral powder content is 15 kg (including silicon-aluminum materials), the steel slag powder content is 30 kg, and the solid waste content accounts for 50% of the total solid mass; the water glass content is 2.4 kg, and the organosilicon waterproofing agent content is 0.8 kg, with a mass ratio of 3:1; the carbonization pressure is 1.2 MPa (compliant with P=0.02×35+0.35=1.05, actually slightly higher to verify parameter boundaries), the temperature is 35℃, the relative humidity is 60%, the CO2 concentration is 85%, and the carbonization time is 3 hours. The remaining raw materials and preparation process are the same as in Example 1.

[0040] Example 4

[0041] The difference between this embodiment and Example 1 is as follows: the fly ash content is 24 kg, the desulfurization ash content is 36 kg (containing calcium materials), and the solid waste content accounts for 60% of the total solid mass; the water glass content is 2.4 kg, and the organosilicon waterproofing agent content is 0.8 kg, with a mass ratio of 3:1; the carbonization pressure is 2.0 MPa, the temperature is 35℃, the relative humidity is 55%, the CO2 concentration is 99%, and the carbonization time is 4 hours. All other raw materials and preparation processes remain the same as in Example 1.

[0042] Example 5

[0043] The difference between this embodiment and Example 1 is as follows: the fly ash content is 18 kg, the red mud content is 12 kg (containing silicon-aluminum materials), the calcium carbide slag content is 18 kg (containing calcium materials), and the solid waste content accounts for 48% of the total solid mass; the water glass content is 1.92 kg, the urea content is 0.48 kg (inorganic modifier), the organosilicon waterproofing agent content is 0.64 kg, and the hexadecyltrimethylammonium bromide content is 0.32 kg (organic modifier), with an inorganic-organic modifier mass ratio of 3:1; the carbonization pressure is 1.0 MPa, the temperature is 30℃, the relative humidity is 60%, the CO2 concentration is 70%, and the carbonization time is 2.5 h. The remaining raw materials and preparation process are the same as in Example 1.

[0044] Example 6

[0045] The differences between this embodiment and Example 1 are as follows: the fly ash content is 12 kg, the mineral powder content is 18 kg, the steel slag powder content is 12 kg, the calcium carbide slag content is 18 kg, and the solid waste content accounts for 50% of the total solid mass; the water glass content is 2.0 kg, the caustic soda content is 0.5 kg, the organosilicon waterproofing agent content is 0.75 kg, the hexadecyltrimethylammonium bromide content is 0.25 kg, and the inorganic-organic modifier mass ratio is 3.33:1; the carbonization pressure is 1.1 MPa, the temperature is 32℃, the relative humidity is 58%, the CO2 concentration is 75%, and the carbonization time is 3 h. All other raw materials and preparation processes remain the same as in Example 1.

[0046] Example 7

[0047] The difference between this embodiment and Example 1 is as follows: the fly ash content is 25 kg, the red mud content is 5 kg, the desulfurization ash content is 20 kg, and the solid waste content accounts for 50% of the total solid mass; the water glass content is 2.25 kg, the urea content is 0.75 kg, the organosilicon waterproofing agent content is 0.75 kg, the hexadecyltrimethylammonium bromide content is 0.75 kg, and the inorganic-organic modifier mass ratio is 2:1; the carbonization pressure is 1.0 MPa, the temperature is 30℃, the relative humidity is 60%, the CO2 concentration is 80%, and the carbonization time is 3 h. All other raw materials and preparation processes remain the same as in Example 1.

[0048] Comparative Example 1

[0049] The difference between this comparative example and Example 1 is that the carbonization curing step is omitted, while the remaining raw materials and preparation process remain the same as in Example 1. That is, the S4 curing process is performed directly after step S2, and the S3 carbonization curing step is omitted.

[0050] Comparative Example 2

[0051] The difference between this comparative example and Example 1 is that only an inorganic modifier (2.0 kg of water glass) was used, and no organic modifier was added. The other raw materials and preparation process remained the same as in Example 1.

[0052] Comparative Example 3

[0053] The difference between this comparative example and Example 1 is that only an organic modifier (2.0 kg of hexadecyltrimethylammonium bromide) was used, and no inorganic modifier was added. The other raw materials and preparation process remained the same as in Example 1.

[0054] Comparative Example 4

[0055] The difference between this comparative example and Example 1 is that the amount of solid waste added is 10% (lower than the lower limit of the parameter), while the other raw materials and preparation process are the same as in Example 1.

[0056] Comparative Example 5

[0057] The difference between this comparative example and Example 1 is that the amount of solid waste added is 65% (higher than the upper limit of the parameter), while the other raw materials and preparation process are the same as in Example 1.

[0058] Comparative Example 6

[0059] The difference between this comparative example and Example 1 is that the modifier dosage is 0.05% (below the lower limit of the parameter), while the other raw materials and preparation process remain the same as in Example 1.

[0060] Performance testing

[0061] After 7 days of curing, the modified expansive soils prepared in all examples and comparative examples underwent the following performance tests: 1. Free expansion rate test: Refer to GB / T 50123-2019 "Standard for Geotechnical Test Methods" to determine the volume change rate of soil samples after free expansion in pure water.

[0062] 2. Unconfined compressive strength test: In accordance with GB / T 50123-2019, a cylindrical specimen with a diameter of 39.1 mm and a height of 80 mm was prepared, and the unconfined compressive strength at 7 days and 28 days was measured.

[0063] 3.24h No-load swelling rate test: Refer to TB 10102-2010 "Code for Geotechnical Testing of Railway Engineering" to determine the volume swelling rate of soil samples after immersion in water for 24 hours under no-load conditions.

[0064] 4. Optimal moisture content and maximum dry density test: determined by standard compaction test according to GB / T 50123-2019.

[0065] The results are shown in Table 1: Table 1

[0066] As shown in Table 1, the free expansion rate of all examples (1-7) was significantly reduced to 27.8-31.5%, which is more than 50% lower than that of plain soil (68.2%); the 24-hour unloaded expansion rate was reduced to 2.6-4.2%, which is 67-80% lower than that of plain soil (12.8%); the 7-day unconfined compressive strength reached 1.0-1.5 MPa, which is 67-150% higher than that of plain soil (0.6 MPa); and the 28-day unconfined compressive strength reached 1.8-2.5 MPa, indicating that the modified soil has excellent strength development characteristics.

[0067] Example 3 exhibited the best overall performance, with the lowest free expansion rate (28.2%), the highest 7-day and 28-day compressive strength (1.5 MPa and 2.5 MPa), and the lowest 24-hour no-load expansion rate (2.8%). This is closely related to its higher solid waste content (50%) and optimized carbonization parameters (1.2 MPa, 35°C), indicating that appropriately increasing the solid waste content and optimizing carbonization conditions within the parameter range can further enhance the modification effect. Examples 5 and 6 demonstrate the effects of different modifier combinations. Example 5 used urea to replace part of the water glass, while Example 6 used caustic soda and adjusted the proportion of organic modifiers. The performance of both examples is close to that of Example 3, illustrating the universality of the technical solution of this invention.

[0068] In contrast, Comparative Example 1 (without carbonization curing) showed significantly higher free expansion rate (52.3%) and 24-hour unloaded expansion rate (9.5%) than the Examples, indicating that carbonization curing plays a decisive role in the formation of carbonate precipitates and the reduction of expansion. The performance of Comparative Example 2 (inorganic modification only) and Comparative Example 3 (organic modification only) was lower than that of the Examples. In particular, Comparative Example 3 had a high free expansion rate of 45.7%, a 24-hour unloaded expansion rate of 8.2%, and a 7-day strength of only 0.65 MPa, far below the average level of the Examples, confirming the synergistic effect of organic-inorganic composite modification.

[0069] Comparative Example 4 (10% solid waste content) showed a free expansion rate (58.7%) close to that of the native soil, and a relatively high 24-hour unloaded expansion rate (10.3%), indicating that an insufficient amount of additive could not provide enough active ingredients to participate in the reaction, resulting in limited modification effects. Comparative Example 5 (65% solid waste content), while showing relatively low free expansion rates (35.6%) and 24-hour unloaded expansion rates (5.1%), had a lower 7-day unconfined compressive strength (0.95 MPa) than the example, indicating that an excessively high amount of additive would lead to a loose soil structure and limited strength development. Comparative Example 6 (0.05% modifier content) showed high free expansion rates (47.3%) and 24-hour unloaded expansion rates (8.5%), but low strength, indicating that an insufficient amount of modifier could not effectively regulate the pH and surface properties of the system, affecting the carbonation reaction efficiency.

[0070] Optimal moisture content data showed that the optimal moisture content of all embodiments increased to 22.5-23.4%, an increase of 3.4-4.3 percentage points compared to the original soil (19.1%), indicating that the modified soil had enhanced water-holding capacity, which is beneficial to vegetation growth. Regarding maximum dry density, the dry density of the embodiments (1.50-1.57 g / cm³) was slightly lower than that of the original soil (1.63 g / cm³), indicating that the modified soil structure was more porous and the porosity increased. This is consistent with the dual effect of carbonate precipitation filling some pores while the organic modifier reduces interparticle attraction.

[0071] Comprehensive analysis shows that this invention successfully solves the engineering challenges of expansive soil through the synergistic effect of organic-inorganic composite modification and precise carbonation curing. Precise control of carbonation process parameters ensures efficient CO2 utilization, while the rational ratio of organic-inorganic modifiers achieves synergistic optimization of strength enhancement and expansibility reduction. The scientific utilization of solid waste balances engineering benefits with resource recycling. Comparisons between the examples and comparative examples fully demonstrate the necessity and synergistic effect of each technical feature in this invention, providing an innovative solution for the engineering treatment of expansive soil.

[0072] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. An expansive soil based on organic-inorganic composite modification and carbonation curing, characterized in that, It is prepared by carbonization curing of expansive soil, solid waste and modifier, wherein the solid waste accounts for 15-60% of the total mass of expansive soil and solid waste, and the modifier accounts for 0.1-5% of the total mass of expansive soil and solid waste; the solid waste includes at least two of fly ash, steel slag powder, mineral powder, carbide slag, red mud and desulfurization ash; the modifier includes at least two of water glass, urea, caustic soda, hexadecyltrimethylammonium bromide and organosilicon waterproofing agent.

2. The expansive soil based on organic-inorganic composite modification and carbonation curing according to claim 1, characterized in that, The solid waste contains at least one calcium-containing material and one silicon-aluminum-containing material, with a mass ratio of (1-3):1; the calcium-containing material is one of steel slag powder, carbide slag, and desulfurization ash; the silicon-aluminum-containing material is one of fly ash, mineral powder, and red mud.

3. The expansive soil based on organic-inorganic composite modification and carbonation curing according to claim 1, characterized in that, The modifier comprises at least one inorganic modifier and one organic modifier, with a mass ratio of (2-4):1; the inorganic modifier is one of water glass, urea and caustic soda; the organic modifier is one of hexadecyltrimethylammonium bromide and organosilicon waterproofing agent.

4. The expansive soil based on organic-inorganic composite modification and carbonation curing according to claim 1, characterized in that, During the carbonization curing process, the CO2 pressure is 0.5-2 MPa, the temperature is 25-35℃, the relative humidity is 55-65%, and the CO2 concentration is 40-99%.

5. The expansive soil based on organic-inorganic composite modification and carbonation curing according to claim 1, characterized in that, During the carbonization curing process, the CO2 pressure and temperature satisfy the following relationship: P = 0.02T + 0.35, where P is the pressure and T is the temperature; The relationship between relative humidity and CO2 concentration is: H = -0.35C + 82.5, where H is the relative humidity and C is the CO2 concentration.

6. The expansive soil based on organic-inorganic composite modification and carbonation curing according to claim 1, characterized in that, The mass ratio of hexadecyltrimethylammonium bromide to organosilicon waterproofing agent in the organic modifier is (1-3):

1.

7. A method for preparing expansive soil based on organic-inorganic composite modification and carbonation curing, characterized in that, The method for preparing the expansive soil based on organic-inorganic composite modification and carbonization curing as described in any one of claims 1-6 comprises the following steps: S1. Material pretreatment: Weigh out expansive soil, solid waste, and modifier according to the specified proportions, where solid waste accounts for 15-60% of the total mass of expansive soil and solid waste, and modifier accounts for 0.1-5% of the total mass of expansive soil and solid waste; S2. Mixing and blending: Mix the materials from step S1 in a mixing container for 5-30 minutes to form a homogeneous mixture; S3. Carbonization curing: Introduce CO2 into the mixing container, control the carbonization pressure at 0.5-2MPa, the temperature at 25-35℃, the relative humidity at 55-65%, and the CO2 concentration at 40-99%, and continue the carbonization reaction. S4. Curing treatment: Curing the carbonized mixture for 8-36 hours to allow the reaction to proceed fully and obtain modified expansive soil.

8. The method for preparing expansive soil based on organic-inorganic composite modification and carbonation curing according to claim 7, characterized in that, In step S1, the liquid limit of the expansive soil is 45-65%, the plasticity index is 20-35, and the free expansion rate is 40-80%.

9. A method for preparing expansive soil based on organic-inorganic composite modification and carbonation curing according to claim 7, characterized in that, The carbonization reaction in step S3 lasts for 1-4 hours.

10. A method for preparing expansive soil based on organic-inorganic composite modification and carbonation curing according to claim 7, characterized in that, In step S4, the ambient temperature for the material curing process is 20-30℃ and the relative humidity is 70-85%.

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