Composite curing agent, planting soil and preparation method and application thereof

Abstract

The application discloses a composite solidifying agent, a planting soil and a preparation method and application thereof, and belongs to the technical field of geotechnical engineering and soil improvement. The composite solidifying agent comprises 38-45 parts of Portland cement, 20-28 parts of slag powder, 15-22 parts of fly ash, 5-10 parts of metakaolin, 3-6 parts of desulfurization gypsum and 4-8 parts of porous biochar. In addition, the application further provides a preparation method of the composite solidifying agent, which comprises the following steps: mixing and dry-mixing Portland cement, slag powder, fly ash, metakaolin, desulfurization gypsum and porous biochar, then adding nano silicon dioxide and humic acid salt to continue mixing and dry-mixing, and then spraying polycarboxylate superplasticizer to continue wet-mixing. The application further provides a planting soil which comprises a planting soil base material and the composite solidifying agent. In addition, the application further provides application of the planting soil in ecological restoration. The application realizes the significant improvement of the strength without sacrificing the ecological function.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering and soil improvement technology, specifically to a composite curing agent, planting soil, its preparation method, and its application. Background Technology

[0002] With the deepening of urbanization and ecological restoration projects, the demand for engineering soil, a key material for infrastructure construction, continues to rise. However, traditional soil extraction methods easily lead to environmental problems such as farmland damage, ecological degradation, and soil erosion, making the resource-based preparation of engineering soil from waste an important direction for sustainable development. Planting soil, due to its excellent water retention, porous structure, and organic matter content, is widely used in soil improvement and vegetation restoration, possessing potential value as an engineering raw material. However, current research mainly focuses on converting solid waste such as silt and construction slurry into planting soil for landscaping purposes, with few explorations of technical pathways that use planting soil itself as a base material and modify it through solidification to meet engineering mechanical performance requirements.

[0003] The preparation of engineering soil with both ecological functions and structural bearing capacity using planting soil requires significantly improving compressive strength, shear strength, and long-term water stability while preserving its biological activity and hydrological characteristics. Existing technologies, such as patent CN109258393A, which prepares high-fertility planting soil by adding lignin sulfonate and fertilizer, optimize the plant growth environment, but its formula lacks reinforcing cementitious components, resulting in low material strength, easy softening upon contact with water, and inability to withstand engineering loads. Patent CN118084287A uses a tube-bag method to dewater silt and directly reuse it as greening soil, achieving volume reduction, but the product is loose and blocky, lacking integrity and compactability, and does not address freeze-thaw resistance, erosion resistance, and other engineering durability indicators. Furthermore, existing processes generally rely on natural curing or simple mixing, resulting in long curing cycles and poor construction adaptability, making it difficult to meet the comprehensive requirements of rapid molding, high density, and long-term stability in scenarios such as roadbed filling and slope protection.

[0004] Therefore, there is an urgent need for a method that can efficiently transform planting soil into a solidification and treatment method that meets engineering performance standards, and systematically solve key technical bottlenecks such as insufficient strength, weak durability and poor process adaptability without sacrificing its ecological function. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a composite curing agent, planting soil, its preparation method and application, thereby solving the technical problem of insufficient strength in the prior art without sacrificing its ecological function.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a composite curing agent, which, by weight, comprises 38-45 parts silicate cement, 20-28 parts slag powder, 15-22 parts fly ash, 5-10 parts metakaolin, 3-6 parts desulfurized gypsum, 4-8 parts porous biochar, 1-1.8 parts nano silica, 0.5-1.5 parts humate, and 0.6-1 parts polycarboxylate superplasticizer.

[0007] In addition, the present invention also proposes a method for preparing the above-mentioned composite curing agent, comprising the following steps: mixing silicate cement, slag powder, fly ash, metakaolin, desulfurized gypsum and porous biochar and dry mixing for 2-4 minutes, then adding nano silica and humate and continuing to mix and dry mix for 1-3 minutes, then spraying in polycarboxylate water-reducing agent and continuing to wet mix for 2-4 minutes.

[0008] In addition, the present invention also proposes a planting soil, comprising a planting soil substrate and the above-mentioned composite curing agent; the mass ratio of the planting soil substrate to the composite curing agent is (8-10):1, and the moisture content of the planting soil substrate is 15%-27%.

[0009] In addition, the present invention also proposes a method for preparing the above-mentioned planting soil, comprising the following steps: mixing the planting soil substrate with a composite curing agent, replenishing water in the form of atomized water, and adjusting the moisture content of the planting soil substrate by air drying.

[0010] In any embodiment, an air-entraining agent is added after mixing.

[0011] In any embodiment, the air-entraining agent is a rosin soap; and / or, the amount of the rosin soap added is 0.2-0.4% of the total mass of the planting soil substrate and the composite curing agent.

[0012] In any embodiment, after mixing, a coagulant accelerator is added; and / or, the amount of the coagulant accelerator added is 0.4%-0.6% of the total mass of the planting soil substrate and the composite curing agent.

[0013] In any embodiment, the coagulant is sodium aluminate.

[0014] Furthermore, this invention also proposes the application of the above-mentioned planting soil or the planting soil prepared by the above-mentioned method in ecological restoration.

[0015] In any implementation, the method includes: layering planting soil, followed by steam curing at 55-65°C for 20-36 hours, and then natural curing for more than 7 days.

[0016] Compared with existing technologies, the beneficial effects of this invention include: by constructing an ecological composite curing agent system with silicate cement, slag powder, fly ash and metakaolin as the cementitious skeleton, desulfurized gypsum to activate potential activity, nano-silica to fill micropores and promote CSH gel formation, and porous biochar and humic acid salts to maintain water retention, air permeability and rhizosphere-friendly environment, the combined use of this system with planting soil substrate effectively solves the problems of excessive alkalinity, pore blockage and reduced plant survival rate caused by simply increasing cement content. This enables the 28-day unconfined compressive strength to reach or exceed the preset 28-day strength target value, while maintaining the hydraulic conductivity, pH value and root penetration capacity required for vegetation growth, thus significantly improving strength without sacrificing its ecological function.

[0017] While significantly improving mechanical properties, this invention controls the organic matter retention rate and pore structure, so that the engineering soil still has good water retention, air permeability and biocompatibility. The saturated hydraulic conductivity is maintained above the preset hydraulic conductivity threshold. The proposed planting soil can be directly used in vegetation restoration projects without the need for an additional planting layer, realizing the integrated design of "structure-ecology" and expanding the application scenarios of engineering soil in green infrastructure, sponge city and ecological restoration.

[0018] The planting soil proposed in this invention uses planting soil substrate as raw material, avoiding the damage to arable land caused by traditional soil extraction. At the same time, it uses industrial solid waste (fly ash, slag) as auxiliary cementing material to achieve efficient resource recycling. The engineering soil produced has no harmful substances released, and the pH value is stable within the preset pH value range, which has no inhibitory effect on plant growth and is in line with the development direction of green building materials and sustainable engineering.

[0019] This invention employs conventional geotechnical mixing and compaction equipment, combined with a controllable steam curing process. The curing cycle is shortened to the time required to achieve the predetermined initial strength, which significantly speeds up the process compared to traditional natural curing and is suitable for rapid on-site construction. The layered filling and vibration compaction parameters are clearly defined, and the compaction degree is consistently above the preset compaction degree threshold, meeting the requirements of engineering filling specifications and solving the problem of loose and difficult-to-compact products in existing technologies. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of the method for preparing planting soil according to Embodiment 1 of the present invention. Detailed Implementation

[0021] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0022] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0023] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0024] This specific embodiment provides a composite curing agent, comprising 38-45 parts silicate cement, 20-28 parts slag powder, 15-22 parts fly ash, 5-10 parts metakaolin, 3-6 parts desulfurized gypsum, 4-8 parts porous biochar, 1-1.8 parts nano-silica, 0.5-1.5 parts humate, and 0.6-1 part polycarboxylate superplasticizer; wherein, the silicate cement is P·O 42.5 grade ordinary silicate cement; the slag powder is an S95 grade product with a specific surface area of ​​not less than 420 square meters / kg; and the fly ash conforms to GB / T The fly ash is Grade I or II according to the 1596 standard; the total amount of activated alumina and silica in metakaolin is not less than 85%; the calcium sulfate dihydrate content in desulfurized gypsum is not less than 90%; the porous biochar is obtained by oxygen-limited pyrolysis of garden branches or straw at 450℃ to 550℃, with a particle size of 0.075 mm to 1 mm, an iodine adsorption value of not less than 500 mg / g, and a pH value of 7.0 to 9.0; the nano silica has an average particle size of 20 nm and a specific surface area greater than 200 m² / g; the humate is potassium humate or sodium humate.

[0025] This specific embodiment also proposes a method for preparing a composite curing agent, including the following steps: mixing silicate cement, slag powder, fly ash, metakaolin, desulfurized gypsum and porous biochar and dry mixing for 2-4 minutes, then adding nano silica and humate and continuing to mix and dry mix for 1-3 minutes, then spraying in polycarboxylate-based water-reducing agent and continuing to wet mix for 2-4 minutes.

[0026] This specific embodiment also proposes a planting soil, including a planting soil substrate and the above-mentioned composite curing agent; the mass ratio of the planting soil substrate to the composite curing agent is (8-10):1, and the moisture content of the planting soil substrate is 15%-27%.

[0027] This specific embodiment also proposes a method for preparing planting soil, including the following steps: mixing planting soil substrate with a composite curing agent, replenishing water in the form of atomized water, and adjusting the moisture content of planting soil substrate by air drying.

[0028] In some embodiments, after mixing, an air-entraining agent is added, which is a rosin soap, and the amount of rosin soap added is 0.2-0.4% of the total mass of the planting soil substrate and the composite curing agent.

[0029] In some embodiments, after mixing, an accelerator is added, wherein the accelerator is sodium aluminate, and the amount of accelerator added is 0.4%-0.6% of the total mass of the planting soil substrate and the composite curing agent.

[0030] This specific embodiment also proposes the application of the above-mentioned planting soil or the planting soil prepared by the above-mentioned method in ecological restoration, including: layering planting soil, steam curing at 55-65℃ for 20-36 hours, and then natural curing for more than 7 days.

[0031] The main challenge facing this invention is that: firstly, organic matter in the planting soil adsorbs calcium. 2+ First, the cement content coats soil particles, inhibiting cement hydration and the continuous generation of cementitious products, leading to insufficient early strength. Second, while simply increasing the cement content can improve strength, it raises the pH value to above 9.0 and seals interconnected pores, resulting in decreased hydraulic conductivity and difficulty for roots to penetrate. Third, excessive amounts of ecological components such as biochar and humic acid weaken the skeleton strength and increase compaction rebound. Therefore, this invention improves strength, permeability, water retention, and rhizosphere suitability simultaneously within a usable range through a combination of "low cement clinker + secondary reaction of mineral admixtures + nano-induced nucleation + porous biochar for pore preservation + humic acid salt for alkalinity buffering".

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] In this invention, the terms "some embodiments," "this embodiment," and examples are used to describe a subset of all possible embodiments. However, it is understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with each other without conflict.

[0034] If the application documents contain similar descriptions such as "first / second", the following explanation shall be added: In the following description, the terms "first / second / third" are used only to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein.

[0035] In this embodiment, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, object A and / or object B can represent three situations: object A exists alone, object A and object B exist simultaneously, and object B exists alone.

[0036] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0037] Example 1

[0038] This embodiment proposes a composite curing agent, which, by weight, comprises 40 parts silicate cement, 25 parts slag powder, 18 parts fly ash, 7 parts metakaolin, 4 parts desulfurized gypsum, 6 parts porous biochar, 1.4 parts nano-silica, 1 part potassium humate, and 0.8 parts polycarboxylate superplasticizer. The silicate cement used is P·O 42.5 grade ordinary silicate cement; the slag powder is an S95 grade product with a specific surface area of ​​not less than 420 square meters / kg; and the fly ash conforms to GB / T... The fly ash is Grade I or II according to the 1596 standard; the total amount of activated alumina and silica in metakaolin is not less than 85%; the calcium sulfate dihydrate content in desulfurized gypsum is not less than 90%; the porous biochar has a particle size of 0.075 mm to 1 mm, an iodine adsorption value of not less than 500 mg / g, and a pH value of 7.0 to 9.0; the average particle size of nano-silica is 20 nm, and the specific surface area is greater than 200 m² / g; the humate is potassium humate.

[0039] The composite curing agent proposed in this embodiment is prepared by the following steps: Silicate cement, slag powder, fly ash, metakaolin, desulfurized gypsum, and porous biochar are added to a high-speed planetary mixer according to their mass proportions and dry-mixed for 3 minutes to ensure thorough and uniform mixing of the cementing components and porous water-retaining components. Subsequently, nano-silica and potassium humate are added, and dry-mixing continues for 2 minutes to ensure uniform dispersion of the nano-active components and rhizosphere buffer components. Finally, a polycarboxylate-based water-reducing agent is sprayed into the mixer in atomized form and wet-mixed for 3 minutes to form a low-alkali, pore-preserving, and root-promoting ecological composite curing agent. The cement content in the formula is reduced by approximately 20% to 35% compared to a single cement curing system. Slag, fly ash, and metakaolin jointly compensate for later-stage strength, porous biochar retains interconnected pores and adsorbs nutrients, and humate buffers alkalinity and improves the plant rhizosphere environment.

[0040] This embodiment also proposes a planting soil, combined with... Figure 1 It is prepared by the following steps:

[0041] S1. Pretreatment and performance evaluation of the original planting soil, specifically including the following procedures: First, collect original planting soil with good water retention and organic matter content. The source can be compost from landscaping waste, topsoil from farmland, or pre-stabilized urban sludge substrate. Immediately after collection, seal and store in a moisture-proof container to prevent moisture evaporation and organic matter oxidation and degradation. Subsequently, conduct a systematic performance evaluation of the collected original planting soil. This evaluation process covers the determination of four core indicators: moisture content, organic matter content, particle size distribution, and initial unconfined compressive strength.

[0042] Moisture content was determined using the drying method, in accordance with the "Standard for Geotechnical Testing Methods" (GB / T 50123). Approximately 100 grams of representative sample were dried in a constant temperature oven at 105℃±5℃ until constant weight. The percentage of mass loss was calculated as the moisture content value. Organic matter content was determined using the potassium dichromate titration method. The specific procedure was as follows: 0.5 grams of air-dried soil sample (passed through a 0.149 mm sieve) was weighed, and a potassium dichromate-sulfuric acid solution of known concentration was added. The mixture was heated and oxidized under oil bath conditions. After cooling, the remaining potassium dichromate was titrated with a ferrous sulfate standard solution. The organic carbon content was calculated based on the amount consumed and multiplied by 1.724 to convert it to organic matter content. Particle size distribution analysis was performed using a combination of sieving and hydrometer methods. Particles larger than 0.075 mm were dry-sieved using a standard set of sieves (apertures of 2.00 mm, 1.00 mm, 0.50 mm, 0.25 mm, and 0.075 mm, respectively). Particles smaller than 0.075 mm were settled using a hydrometer to determine the settling velocity. A cumulative particle distribution curve was plotted to determine the proportion of each particle group. Initial unconfined compressive strength testing used standard cylindrical specimens with a diameter of 39.1 mm and a height of 80 mm. After standing for 24 hours under standard curing conditions (temperature 20℃±2℃, relative humidity ≥95%), the specimens were demolded and subjected to axial compression at a loading rate of 1 mm / min using a universal testing machine. The peak load was recorded, and the compressive strength value was calculated.

[0043] After completing the above four index measurements, the original planting soil was fed into a vibrating sieve for impurity removal. The sieve mesh size was set to 5 mm, i.e., the preset particle size threshold was 5 mm, effectively removing all impurities such as stones, plant root and stem residues, and plastic fragments with a particle size greater than 5 mm. The sieved material was then conveyed by a belt conveyor into a homogenization mixing chamber and stirred at low speed for 10 minutes to ensure that the physical state of the material was uniform, ultimately obtaining a homogenized planting soil substrate. In this embodiment, the organic matter content of the homogenized planting soil substrate was not less than 3.0%, the moisture content was controlled within the range of 18% to 25%, and the particle size distribution met the requirement that fine-grained soil (particle size less than 0.075 mm) accounted for more than 60%, to ensure that the subsequent solidification reaction had sufficient reaction interface and gelling activity, while retaining sufficient microporous structure to maintain ecological water retention capacity.

[0044] S2. The homogenized planting soil substrate and the composite curing agent of this embodiment are added to a twin-shaft forced mixer at a mass ratio of 90:10. This mixer is equipped with two parallel mixing shafts, each mounted with a combination of helical blades and paddle blades. The rotation speed is adjustable from 30 to 60 rpm. The mixing time is set to 5 minutes, i.e., no less than a preset mixing time threshold of 5 minutes, to ensure that the curing agent particles are uniformly distributed in three-dimensional space within the planting soil matrix, avoiding local enrichment or depletion.

[0045] During the mixing process, the moisture content of the mixture is monitored in real time. The optimal moisture content is determined in advance through a standard compaction test: representative planting soil substrates are taken and mixed with the curing agent at different moisture contents (e.g., 15%, 18%, 21%, 24%, 27%). Samples are prepared using a standard compactor (2.5 kg hammer, 305 mm drop height, three layers, 25 blows per layer). The moisture content corresponding to the maximum dry density is measured, which is the optimal moisture content. Typically, this optimal moisture content is between 20% and 23%. In actual mixing, if the moisture content of the mixture is found to be lower than the lower limit of the optimal moisture content, water is added in the form of atomized water through the top spray system. The atomized particle diameter is controlled between 50 and 100 micrometers to avoid local over-wetting. If the moisture content is higher than the upper limit, the ventilation vents on the side wall of the mixer are opened to introduce dry air at room temperature for drying, with the airflow controlled at 0.5 cubic meters per minute. Through the above-mentioned control methods, the actual moisture content deviation is kept within the preset allowable moisture content deviation range of ±1.0%, thereby ensuring that the mixture has good compactability, which is manifested as a state where it can be formed into a ball when squeezed by hand and crumbles when dropped.

[0046] This embodiment also proposes the application of the aforementioned planting soil in ecological restoration, including: transporting the planting soil to the construction site, unloading it using dump trucks, and then leveling it with a grader to form a single-layer fill layer. The thickness of each layer is controlled within the range of 25 to 30 centimeters, i.e., the predetermined fill thickness range is 25-30 centimeters. This thickness has been verified through field tests to balance compaction efficiency and energy transfer depth. The compaction operation is performed using a high-frequency vibratory roller, with the excitation frequency set to 30 Hz to 35 Hz, the amplitude to 1.2 mm to 1.5 mm, and the travel speed controlled at 2.0 km / h to 3.0 km / h. The number of compaction passes is no less than 6, i.e., the preset minimum number of compaction passes is 6. The first two passes are static pressure stabilization, the middle three passes are high-intensity vibration compaction, and the last pass is static pressure finishing. During the compaction process, the roller's travel trajectory adopts a staggered wheel overlap method, with the overlap width of adjacent compaction strips not less than 20 centimeters, ensuring uniform compaction across the entire cross-section.

[0047] After each layer is compacted, the compaction degree is immediately tested using the sand cone method. The specific procedure is as follows: three test points are randomly selected on the surface of the compacted layer. Test pits with a diameter of 150 mm and a depth equal to the thickness of the fill layer are dug, and all samples are collected and weighed. Simultaneously, the test pits are filled with standard sand, and the volume of the test pits is calculated based on the sand density and the filling volume. The on-site dry density is then calculated. The compaction degree is the ratio of the on-site dry density to the maximum dry density obtained from the standard compaction test. The test results must reach at least 95% of the preset compaction degree threshold before the next layer can be filled. If the compaction degree at a certain point is insufficient, the area is compacted twice and retested until it passes.

[0048] During the layered filling process, a 2 mm thick interface treatment layer is set between adjacent layers. This treatment layer is formed by applying pure cement slurry with a water-cement ratio of 0.45 using a high-pressure airless spraying device at a spraying pressure of 0.6 MPa and a nozzle distance of 30 cm from the surface of the lower layer, forming a continuous and uniform thin layer. This interface treatment layer forms chemical bonds and mechanical interlocking between the upper and lower layers of the mixture, significantly enhancing interlayer adhesion, preventing interlayer slippage under shear loads, and improving the overall structural stability.

[0049] Immediately cover the compacted soil with an insulating and moisture-retaining membrane, and then place a movable, sealed insulating and moisture-retaining curing cover over the compacted soil area to create a sealed curing space. Introduce steam into this sealed curing space for on-site steam curing. The curing temperature is controlled at 60℃ (preset curing temperature), the relative humidity is not lower than 95% (preset humidity threshold), and the curing duration is 24 hours.

[0050] During the heating phase, programmed temperature control is employed, with the heating rate kept below 10℃ / hour. This is a preset heating rate threshold of 10℃ / hour to prevent micro-cracks caused by thermal stress concentration due to excessive temperature differences between the inside and outside. After the heat preservation phase, the surface is cooled to room temperature at the same rate, then the covering film is removed, and the surface is placed in a natural curing environment. The natural curing period is no less than 7 days, meaning the predetermined natural curing period is 7 days. During this period, the surface is kept moist, sprayed with water twice daily to prevent excessive evaporation from affecting the subsequent hydration reaction.

[0051] After curing, the performance of the soil used in the project was verified. The unconfined compressive strength at 7 days was no less than 1.2 MPa, the strength at 28 days was no less than 2.5 MPa, and the strength retention rate after 72 hours of immersion in water was greater than 85%. Furthermore, the soil used in this project retained the porous structure characteristics of planting soil, with a saturated hydraulic conductivity of no less than 1×10⁻⁶. -5With a flow rate of 3 m / s, it supports the root penetration and growth of herbaceous plants, making it suitable for composite functional scenarios such as ecological slope protection, green roadbeds, and vegetated concrete base courses. In freeze-thaw cycle tests, after undergoing 25 freeze-thaw cycles (freezing at -20℃ for 4 hours and thawing at +20℃ for 4 hours as one cycle), the mass loss rate is less than 3.0%, and the strength loss rate is less than 15%. In erosion resistance tests, after being eroded by a water flow of 3 m / s for 2 hours, the surface erosion depth is less than 5 mm.

[0052]

[0053] Among them, f wet f is the unconfined compressive strength after immersion in water. dry This refers to the unconfined compressive strength after standard curing.

[0054]

[0055] Where Q is the volume of water passing through the sample per unit time (cubic meters), L is the sample length (meters), A is the cross-sectional area (square meters), t is the time (seconds), and h is the head difference (meters).

[0056] To further verify the engineering applicability of this embodiment, another specific application example is constructed: an urban ecological slope protection project with a designed slope height of 5 meters and a slope ratio of 1:1.5. The requirements are that the 28-day compressive strength of the filling material be ≥2.0 MPa and the saturated hydraulic conductivity be ≥5×10⁻⁶. -6 Meters per second, and can support the growth of bermudagrass seeds.

[0057] Before construction, local landscaping waste compost was collected as the initial planting soil. Testing revealed an organic matter content of 4.2%, a moisture content of 22%, a fine-grained soil ratio of 68%, a pH of 7.4, and an initial unconfined compressive strength of 0.15 MPa. The planting soil, as described in this embodiment, was layered to a thickness of 28 cm and compacted seven times with a high-frequency vibratory roller at 32 Hz, 1.3 mm amplitude, and a speed of 2.5 km / h. The compaction degree of each layer was measured to be over 96%. A 2 mm interface layer was formed by spraying a 0.45 water-cement ratio cement-fly ash slurry between layers. After 24 hours of low-temperature steam curing at 55℃, natural moisture curing was carried out for 7 days.

[0058] The final product achieved a compressive strength of 2.7 MPa after 28 days and a saturated water conductivity of 1.2 × 10⁻⁶. -5 With a speed of m / s, a pH of 7.8, a strength retention rate of 88% after 72 hours of immersion in water, and a strength loss rate of 12% after 25 freeze-thaw cycles, it fully meets the design requirements. After sowing Bermuda grass seeds, the germination rate reaches 90% in 30 days, the coverage rate exceeds 85% in 60 days, and the root penetration depth reaches 15 cm, proving that it has both engineering load-bearing and ecological functions.

[0059] Comparative Example 1

[0060] The difference between the planting soil in this comparative example and Example 1 in ecological restoration is that the planting soil was not solidified, that is, no solidifying agent was added; otherwise, it was the same as Example 1.

[0061] Comparative Example 2

[0062] The difference between the application of the planting soil in this comparative example in ecological restoration and Example 1 is that the composite curing agent is replaced with an equal amount of ordinary silicate cement in the planting soil, while everything else is the same as in Example 1.

[0063] Comparative Example 3

[0064] The composite curing agent in this comparative example, calculated by mass parts, includes 50 parts cement, 30 parts fly ash, 20 parts slag, and 1.5 parts nano silica; the planting soil in this comparative example and the relevant steps in its application in ecological restoration are the same as in Example 1.

[0065] Comparative Example 4

[0066] The composite curing agent in this comparative example, calculated by mass parts, includes 50 parts cement, 30 parts fly ash, 20 parts slag, 1.5 parts nano silica, and 10 parts porous biochar.

[0067] The planting soil and related steps in the application of planting soil in ecological restoration in this comparative example are the same as those in Example 1.

[0068] Table 1. Comparison of strength and ecological function data for different curing agent formulations.

[0069]

[0070] As shown in Table 1, although Comparative Examples 2 and 3 exhibited high compressive strength, their hydraulic conductivity, pH value, and plant growth indicators were significantly deteriorated. Comparative Example 4 improved ecological indicators, but its strength and water stability were insufficient due to an excessively high biochar ratio and a lack of mineral activation. Example 1 of this invention demonstrated a 28-day strength of 2.70 MPa, a water immersion strength retention rate of 89%, a saturated hydraulic conductivity of 1.2 × 10⁻⁵ m / s, a pH value of 7.8, a 30-day germination rate of 90%, and a root penetration depth of 15 cm at 60 days, indicating that it retained pores, moisture, and a rhizosphere environment suitable for plant growth while meeting engineering load-bearing requirements.

[0071] Example 2

[0072] This embodiment proposes a composite curing agent, which, by weight, comprises 42 parts silicate cement, 26 parts slag powder, 15 parts fly ash, 6 parts metakaolin, 5 parts desulfurized gypsum, 6 parts porous biochar, 1.6 parts nano-silica, 0.8 parts potassium humate, and 0.9 parts polycarboxylate superplasticizer. The silicate cement used is P·O 42.5 grade ordinary silicate cement; the slag powder is an S95 grade product with a specific surface area of ​​not less than 420 square meters / kg; and the fly ash conforms to GB / T... The fly ash is Grade I or II according to the 1596 standard; the total amount of activated alumina and silica in metakaolin is not less than 85%; the calcium sulfate dihydrate content in desulfurized gypsum is not less than 90%; the porous biochar has a particle size of 0.075 mm to 1 mm, an iodine adsorption value of not less than 500 mg / g, and a pH value of 7.0 to 9.0; the average particle size of nano-silica is 20 nm, and the specific surface area is greater than 200 m² / g; the humate is potassium humate.

[0073] The composite curing agent proposed in this embodiment is prepared by the following steps: Silicate cement, slag powder, fly ash, metakaolin, desulfurized gypsum, and porous biochar are added to a high-speed planetary mixer according to their mass proportions and dry-mixed for 3 minutes to ensure thorough and uniform mixing of the cementing components and porous water-retaining components. Subsequently, nano-silica and potassium humate are added, and dry-mixing continues for 2 minutes to ensure uniform dispersion of the nano-active components and rhizosphere buffer components. Finally, a polycarboxylate-based water-reducing agent is sprayed into the mixer in atomized form and wet-mixed for 3 minutes to form a low-alkali, pore-preserving, and root-promoting ecological composite curing agent. The cement content in the formula is reduced by approximately 20% to 35% compared to a single cement curing system. Slag, fly ash, and metakaolin jointly compensate for later-stage strength, porous biochar retains interconnected pores and adsorbs nutrients, and humate buffers alkalinity and improves the plant rhizosphere environment.

[0074] This embodiment also proposes a planting soil, which is prepared by the following steps:

[0075] S1. The original planting soil (planting soil substrate) is selected from alpine meadow humus soil, with an organic matter content of 5.0%, a moisture content of 19%, and a fine-grained soil content of 72%.

[0076] S2. The planting soil substrate and the composite curing agent of this embodiment are added to a twin-shaft forced mixer at a mass ratio of 90:10. The moisture content of the mixture is controlled at 20.5%±0.8%, and 0.3% air-entraining agent (rosin soap) is added to introduce micron-level closed air bubbles and improve frost resistance.

[0077] This embodiment also proposes the application of the above-mentioned planting soil in ecological restoration, including: reducing the filling thickness to 22 cm, increasing the number of compaction passes to 8, and reducing the roller travel speed to 1.8 km / h to ensure sufficient energy transfer during compaction under cold conditions. The water-cement ratio of the interface treatment layer is adjusted to 0.40 to enhance bond strength;

[0078] The steam curing temperature was increased to 65℃, but the heating rate was strictly controlled at 8℃ / hour to prevent thermal shock; the curing time was extended to 36 hours to promote full hydration. The natural curing period was extended to 14 days, and the area was covered with an insulating blanket.

[0079] Testing showed that the design achieved a strength of 2.9 MPa after 28 days, a mass loss rate of 2.5% after 50 freeze-thaw cycles, a strength loss rate of 13%, and an erosion depth of only 3.8 mm after 2 hours of water flow at 3 m / s. The saturated hydraulic conductivity was 9 × 10⁻⁻⁻⁶. 6 The speed of meters per second has been successfully applied to the subgrade project of an ecological highway on the Qinghai-Tibet Plateau.

[0080] Example 3

[0081] This embodiment proposes a composite curing agent, which, by weight, comprises 38 parts silicate cement, 24 parts slag powder, 22 parts fly ash, 6 parts metakaolin, 4 parts desulfurized gypsum, 6 parts porous biochar, 1.2 parts nano-silica, 1.2 parts sodium humate, and 0.7 parts polycarboxylate superplasticizer; wherein, the silicate cement is P·O 42.5 grade ordinary silicate cement; and the fly ash conforms to GB / T The product consists of Grade I or II fly ash according to standard 1596; metakaolin containing no less than 85% total active alumina and silica; desulfurized gypsum containing no less than 90% calcium sulfate dihydrate; porous biochar with a particle size of 0.075 mm to 1 mm, an iodine adsorption value of no less than 500 mg / g, and a pH value of 7.0 to 9.0; nano-silica with an average particle size of 20 nm and a specific surface area greater than 200 m² / g; fly ash and sodium humate enhance pH buffering capacity, porous biochar adsorbs salts and improves the rhizosphere water and air environment, and slag powder with a specific surface area increased to 450 m² / kg to enhance density and block chloride ion penetration.

[0082] The preparation method of the composite curing agent proposed in this embodiment is the same as that in Embodiment 1.

[0083] This embodiment also proposes a planting soil, which is prepared by the following steps:

[0084] S1. The original planting soil is coastal silt-based planting soil after desalination treatment, with an organic matter content of 3.5%, a moisture content of 24%, and a fine-grained soil content of 65%.

[0085] S2. The planting soil substrate and the composite curing agent of this embodiment are added into a twin-shaft forced mixer at a mass ratio of 90:10. The moisture content of the mixture is controlled at 22.0%±1.0%, and 0.5% sodium aluminate is added as a coagulant to accelerate the formation of early strength to resist salt erosion.

[0086] This embodiment also proposes the application of the above-mentioned planting soil in ecological restoration, including: filling with a thickness of 27 cm, compacting 6 times, and using cement-fly ash slurry (1:1) with a water-cement ratio of 0.50 for the interface layer to improve the interface performance against salt corrosion.

[0087] Steam curing at 60℃ for 24 hours, followed by natural curing for 10 days. The final product exhibits a strength of 2.6 MPa after 28 days, a pH of 7.5–8.0, and a strength retention rate of 82% after 90 days of immersion in water (simulated seawater immersion), with a saturated hydraulic conductivity of 1.1 × 10⁻⁶. -5 With a speed of meters per second, it was successfully used in the ecological bank protection project of the Yellow River Delta, and the survival rate of Suaeda salsa planted reached 88%.

[0088] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A composite curing agent, characterized in that, Calculated by weight, it includes 38-45 parts silicate cement, 20-28 parts slag powder, 15-22 parts fly ash, 5-10 parts metakaolin, 3-6 parts desulfurized gypsum, 4-8 parts porous biochar, 1-1.8 parts nano silica, 0.5-1.5 parts humate, and 0.6-1 parts polycarboxylate superplasticizer.

2. A method for preparing the composite curing agent according to claim 1, characterized in that, The process includes the following steps: mixing silicate cement, slag powder, fly ash, metakaolin, desulfurized gypsum and porous biochar in a dry mix for 2-4 minutes, then adding nano-silica and humate and continuing to mix in a dry mix for 1-3 minutes, and finally spraying in polycarboxylate superplasticizer and continuing to wet mix for 2-4 minutes.

3. A type of planting soil, characterized in that, It includes a planting soil substrate and the composite curing agent as described in claim 1; the mass ratio of the planting soil substrate to the composite curing agent is (8-10):1, and the moisture content of the planting soil substrate is 15%-27%.

4. A method for preparing planting soil according to claim 3, characterized in that, The process includes the following steps: mixing the planting soil substrate with the composite curing agent, replenishing water in the form of atomized water, and adjusting the moisture content of the planting soil substrate by air drying.

5. The method for preparing planting soil according to claim 4, characterized in that, The process also includes adding an air-entraining agent after mixing.

6. The method for preparing planting soil according to claim 5, characterized in that, The air-entraining agent is a rosin soap; and / or, the amount of the rosin soap added is 0.2-0.4% of the total mass of the planting soil substrate and the composite curing agent.

7. The method for preparing planting soil according to claim 4, characterized in that, The mixture also includes the addition of a coagulant after mixing; and / or, the amount of the coagulant added is 0.4%-0.6% of the total mass of the planting soil substrate and the composite curing agent.

8. The method for preparing planting soil according to claim 7, characterized in that, The coagulant is sodium aluminate.

9. The application of the planting soil according to claim 3 or the planting soil prepared by any one of claims 4-8 in ecological restoration.

10. The application according to claim 9, characterized in that, include: Layer the planting soil, then steam cure at 55-65℃ for 20-36 hours, followed by natural curing for more than 7 days.

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